Implement actions (#21937)

Close #13539.

Co-authored by: @lunny @appleboy @fuxiaohei and others.

Related projects:
- https://gitea.com/gitea/actions-proto-def
- https://gitea.com/gitea/actions-proto-go
- https://gitea.com/gitea/act
- https://gitea.com/gitea/act_runner

### Summary

The target of this PR is to bring a basic implementation of "Actions",
an internal CI/CD system of Gitea. That means even though it has been
merged, the state of the feature is **EXPERIMENTAL**, and please note
that:

- It is disabled by default;
- It shouldn't be used in a production environment currently;
- It shouldn't be used in a public Gitea instance currently;
- Breaking changes may be made before it's stable.

**Please comment on #13539 if you have any different product design
ideas**, all decisions reached there will be adopted here. But in this
PR, we don't talk about **naming, feature-creep or alternatives**.

### ⚠️ Breaking

`gitea-actions` will become a reserved user name. If a user with the
name already exists in the database, it is recommended to rename it.

### Some important reviews

- What is `DEFAULT_ACTIONS_URL` in `app.ini` for?
  - https://github.com/go-gitea/gitea/pull/21937#discussion_r1055954954
- Why the api for runners is not under the normal `/api/v1` prefix?
  - https://github.com/go-gitea/gitea/pull/21937#discussion_r1061173592
- Why DBFS?
  - https://github.com/go-gitea/gitea/pull/21937#discussion_r1061301178
- Why ignore events triggered by `gitea-actions` bot?
  - https://github.com/go-gitea/gitea/pull/21937#discussion_r1063254103
- Why there's no permission control for actions?
  - https://github.com/go-gitea/gitea/pull/21937#discussion_r1090229868

### What it looks like

<details>

#### Manage runners

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205870657-c72f590e-2e08-4cd4-be7f-2e0abb299bbf.png">

#### List runs

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205872794-50fde990-2b45-48c1-a178-908e4ec5b627.png">


#### View logs

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205872501-9b7b9000-9542-4991-8f55-18ccdada77c3.png">



</details>

### How to try it

<details>

#### 1. Start Gitea

Clone this branch and [install from
source](https://docs.gitea.io/en-us/install-from-source).

Add additional configurations in `app.ini` to enable Actions:

```ini
[actions]
ENABLED = true
```

Start it.

If all is well, you'll see the management page of runners:

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205877365-8e30a780-9b10-4154-b3e8-ee6c3cb35a59.png">


#### 2. Start runner

Clone the [act_runner](https://gitea.com/gitea/act_runner), and follow
the
[README](https://gitea.com/gitea/act_runner/src/branch/main/README.md)
to start it.

If all is well, you'll see a new runner has been added:

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205878000-216f5937-e696-470d-b66c-8473987d91c3.png">

#### 3. Enable actions for a repo

Create a new repo or open an existing one, check the `Actions` checkbox
in settings and submit.

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205879705-53e09208-73c0-4b3e-a123-2dcf9aba4b9c.png">
<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205879383-23f3d08f-1a85-41dd-a8b3-54e2ee6453e8.png">

If all is well, you'll see a new tab "Actions":

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205881648-a8072d8c-5803-4d76-b8a8-9b2fb49516c1.png">

#### 4. Upload workflow files

Upload some workflow files to `.gitea/workflows/xxx.yaml`, you can
follow the [quickstart](https://docs.github.com/en/actions/quickstart)
of GitHub Actions. Yes, Gitea Actions is compatible with GitHub Actions
in most cases, you can use the same demo:

```yaml
name: GitHub Actions Demo
run-name: ${{ github.actor }} is testing out GitHub Actions 🚀
on: [push]
jobs:
  Explore-GitHub-Actions:
    runs-on: ubuntu-latest
    steps:
      - run: echo "🎉 The job was automatically triggered by a ${{ github.event_name }} event."
      - run: echo "🐧 This job is now running on a ${{ runner.os }} server hosted by GitHub!"
      - run: echo "🔎 The name of your branch is ${{ github.ref }} and your repository is ${{ github.repository }}."
      - name: Check out repository code
        uses: actions/checkout@v3
      - run: echo "💡 The ${{ github.repository }} repository has been cloned to the runner."
      - run: echo "🖥️ The workflow is now ready to test your code on the runner."
      - name: List files in the repository
        run: |
          ls ${{ github.workspace }}
      - run: echo "🍏 This job's status is ${{ job.status }}."
```

If all is well, you'll see a new run in `Actions` tab:

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205884473-79a874bc-171b-4aaf-acd5-0241a45c3b53.png">

#### 5. Check the logs of jobs

Click a run and you'll see the logs:

<img width="1792" alt="image"
src="https://user-images.githubusercontent.com/9418365/205884800-994b0374-67f7-48ff-be9a-4c53f3141547.png">

#### 6. Go on

You can try more examples in [the
documents](https://docs.github.com/en/actions/using-workflows/workflow-syntax-for-github-actions)
of GitHub Actions, then you might find a lot of bugs.

Come on, PRs are welcome.

</details>

See also: [Feature Preview: Gitea
Actions](https://blog.gitea.io/2022/12/feature-preview-gitea-actions/)

---------

Co-authored-by: a1012112796 <1012112796@qq.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: delvh <dev.lh@web.de>
Co-authored-by: ChristopherHX <christopher.homberger@web.de>
Co-authored-by: John Olheiser <john.olheiser@gmail.com>

4 files changed, 38 insertions, 3 deletions

diff --git a/docs/content/doc/advanced/config-cheat-sheet.en-us.md b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
index 295fa713a..4ef630b6b 100644
--- a/docs/content/doc/advanced/config-cheat-sheet.en-us.md
+++ b/docs/content/doc/advanced/config-cheat-sheet.en-us.md
@@ -1314,6 +1314,41 @@ PROXY_URL = socks://127.0.0.1:1080
 PROXY_HOSTS = *.github.com
 ```
 
+## Actions (`actions`)
+
+- `ENABLED`: **false**: Enable/Disable actions capabilities
+- `DEFAULT_ACTIONS_URL`: **https://gitea.com**: Default address to get action plugins, e.g. the default value means downloading from "https://gitea.com/actions/checkout" for "uses: actions/checkout@v3"
+
+`DEFAULT_ACTIONS_URL` indicates where should we find the relative path action plugin. i.e. when use an action in a workflow file like
+
+```yaml
+name: versions
+on:
+  push:
+    branches:
+      - main
+      - releases/*
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+```
+
+Now we need to know how to get actions/checkout, this configuration is the default git server to get it. That means we will get the repository via git clone ${DEFAULT_ACTIONS_URL}/actions/checkout and fetch tag v3.
+
+To help people who don't want to mirror these actions in their git instances, the default value is https://gitea.com
+To help people run actions totally in their network, they can change the value and copy all necessary action repositories into their git server.
+
+Of course we should support the form in future PRs like
+
+```yaml
+steps:
+  - uses: gitea.com/actions/checkout@v3
+```
+
+although Github don't support this form.
+
 ## Other (`other`)
 
 - `SHOW_FOOTER_BRANDING`: **false**: Show Gitea branding in the footer.
diff --git a/docs/content/doc/features/comparison.en-us.md b/docs/content/doc/features/comparison.en-us.md
index 1ecbf1068..9eaae36a6 100644
--- a/docs/content/doc/features/comparison.en-us.md
+++ b/docs/content/doc/features/comparison.en-us.md
@@ -56,7 +56,7 @@ _Symbols used in table:_
 | Deploy Tokens                                    | ✓                                                   | ✓    | ✓         | ✓         | ✓         | ✓         | ✓            |
 | Repository Tokens with write rights              | ✓                                                   | ✘    | ✓         | ✓         | ✓         | ✓         | ✓            |
 | RSS Feeds                                        | ✓                                                   | ✘    | ✓         | ✘         | ✘         | ✘         | ✘            |
-| Built-in CI/CD                                   | [✘](https://github.com/go-gitea/gitea/issues/13539) | ✘    | ✓         | ✓         | ✓         | ✘         | ✘            |
+| Built-in CI/CD                                   | ✓                                                   | ✘    | ✓         | ✓         | ✓         | ✘         | ✘            |
 | Subgroups: groups within groups                  | [✘](https://github.com/go-gitea/gitea/issues/1872)  | ✘    | ✘         | ✓         | ✓         | ✘         | ✓            |
 | Interaction with other instances                 | [/](https://github.com/go-gitea/gitea/issues/18240) | ✘    | ✘         | ✘         | ✘         | ✘         | ✘            |
 | Mermaid diagrams in Markdown                     | ✓                                                   | ✘    | ✓         | ✓         | ✓         | ✘         | ✘            |
diff --git a/docs/content/doc/features/comparison.zh-cn.md b/docs/content/doc/features/comparison.zh-cn.md
index c5bec58cb..55014dab7 100644
--- a/docs/content/doc/features/comparison.zh-cn.md
+++ b/docs/content/doc/features/comparison.zh-cn.md
@@ -49,7 +49,7 @@ _表格中的符号含义:_
 | 内置容器 Registry     | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
 | 外部 Git 镜像         | ✓                                                  | ✓    | ✘         | ✘         | ✓         | ✓              | ✓            |
 | WebAuthn (2FA)        | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✓              | ?            |
-| 内置 CI/CD            | ✘                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
+| 内置 CI/CD            | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✘              | ✘            |
 | 子组织：组织内的组织  | [✘](https://github.com/go-gitea/gitea/issues/1872) | ✘    | ✘         | ✓         | ✓         | ✘              | ✓            |
 
 #### 代码管理
diff --git a/docs/content/doc/features/comparison.zh-tw.md b/docs/content/doc/features/comparison.zh-tw.md
index 4da9c74ec..bde177944 100644
--- a/docs/content/doc/features/comparison.zh-tw.md
+++ b/docs/content/doc/features/comparison.zh-tw.md
@@ -51,7 +51,7 @@ menu:
 | 內建 Container Registry  | [✘](https://github.com/go-gitea/gitea/issues/2316) | ✘    | ✘         | ✓         | ✓         | ✘         | ✘            |
 | 對外部 Git 鏡像          | ✓                                                  | ✓    | ✘         | ✘         | ✓         | ✓         | ✓            |
 | FIDO (2FA)               | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✓         | ✘            |
-| 內建 CI/CD               | ✘                                                  | ✘    | ✓         | ✓         | ✓         | ✘         | ✘            |
+| 內建 CI/CD               | ✓                                                  | ✘    | ✓         | ✓         | ✓         | ✘         | ✘            |
 | 子群組: 群組中的群組     | ✘                                                  | ✘    | ✘         | ✓         | ✓         | ✘         | ✓            |
 
 ## 程式碼管理