Support configuration variables on Gitea Actions (#24724)

Co-Author: @silverwind @wxiaoguang 
Replace: #24404

See:
- [defining configuration variables for multiple
workflows](https://docs.github.com/en/actions/learn-github-actions/variables#defining-configuration-variables-for-multiple-workflows)
- [vars
context](https://docs.github.com/en/actions/learn-github-actions/contexts#vars-context)

Related to:
- [x] protocol: https://gitea.com/gitea/actions-proto-def/pulls/7
- [x] act_runner: https://gitea.com/gitea/act_runner/pulls/157
- [x] act: https://gitea.com/gitea/act/pulls/43

#### Screenshoot
Create Variable:

![image](https://user-images.githubusercontent.com/33891828/236758288-032b7f64-44e7-48ea-b07d-de8b8b0e3729.png)


![image](https://user-images.githubusercontent.com/33891828/236758174-5203f64c-1d0e-4737-a5b0-62061dee86f8.png)

Workflow:
```yaml
  test_vars:
    runs-on: ubuntu-latest
    steps:
      - name: Print Custom Variables
        run: echo "${{ vars.test_key }}"
      - name: Try to print a non-exist var
        run: echo "${{ vars.NON_EXIST_VAR }}"
```

Actions Log:

![image](https://user-images.githubusercontent.com/33891828/236759075-af0c5950-368d-4758-a8ac-47a96e43b6e2.png)

---
This PR just implement the org / user (depends on the owner of the
current repository) and repo level variables, The Environment level
variables have not been implemented.
Because
[Environment](https://docs.github.com/en/actions/deployment/targeting-different-environments/using-environments-for-deployment#about-environments)
is a module separate from `Actions`. Maybe it would be better to create
a new PR to do it.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>
Co-authored-by: Giteabot <teabot@gitea.io>

routers/web/web.go

@@ -307,6 +307,15 @@ func registerRoutes(m *web.Route) {
 		m.Post("/packagist/{id}", web.Bind(forms.NewPackagistHookForm{}), repo.PackagistHooksEditPost)
 	}
 
+	addSettingVariablesRoutes := func() {
+		m.Group("/variables", func() {
+			m.Get("", repo_setting.Variables)
+			m.Post("/new", web.Bind(forms.EditVariableForm{}), repo_setting.VariableCreate)
+			m.Post("/{variable_id}/edit", web.Bind(forms.EditVariableForm{}), repo_setting.VariableUpdate)
+			m.Post("/{variable_id}/delete", repo_setting.VariableDelete)
+		})
+	}
+
 	addSettingsSecretsRoutes := func() {
 		m.Group("/secrets", func() {
 			m.Get("", repo_setting.Secrets)
@@ -494,6 +503,7 @@ func registerRoutes(m *web.Route) {
 			m.Get("", user_setting.RedirectToDefaultSetting)
 			addSettingsRunnersRoutes()
 			addSettingsSecretsRoutes()
+			addSettingVariablesRoutes()
 		}, actions.MustEnableActions)
 
 		m.Get("/organization", user_setting.Organization)
@@ -760,6 +770,7 @@ func registerRoutes(m *web.Route) {
 					m.Get("", org_setting.RedirectToDefaultSetting)
 					addSettingsRunnersRoutes()
 					addSettingsSecretsRoutes()
+					addSettingVariablesRoutes()
 				}, actions.MustEnableActions)
 
 				m.RouteMethods("/delete", "GET,POST", org.SettingsDelete)
@@ -941,6 +952,7 @@ func registerRoutes(m *web.Route) {
 				m.Get("", repo_setting.RedirectToDefaultSetting)
 				addSettingsRunnersRoutes()
 				addSettingsSecretsRoutes()
+				addSettingVariablesRoutes()
 			}, actions.MustEnableActions)
 			m.Post("/migrate/cancel", repo.MigrateCancelPost) // this handler must be under "settings", otherwise this incomplete repo can't be accessed
 		}, ctxDataSet("PageIsRepoSettings", true, "LFSStartServer", setting.LFS.StartServer))