add skip ci functionality (#28075)

Adds the possibility to skip workflow execution if the commit message
contains a string like [skip ci] or similar.

The default strings are the same as on GitHub, users can also set custom
ones in app.ini

Reference:
https://docs.github.com/en/actions/managing-workflow-runs/skipping-workflow-runs

Close #28020

docs/content/administration/config-cheat-sheet.en-us.md

@@ -1396,6 +1396,7 @@ PROXY_HOSTS = *.github.com
 - `ZOMBIE_TASK_TIMEOUT`: **10m**: Timeout to stop the task which have running status, but haven't been updated for a long time
 - `ENDLESS_TASK_TIMEOUT`: **3h**: Timeout to stop the tasks which have running status and continuous updates, but don't end for a long time
 - `ABANDONED_JOB_TIMEOUT`: **24h**: Timeout to cancel the jobs which have waiting status, but haven't been picked by a runner for a long time
+- `SKIP_WORKFLOW_STRINGS`: **[skip ci],[ci skip],[no ci],[skip actions],[actions skip]**: Strings committers can place inside a commit message to skip executing the corresponding actions workflow
 
 `DEFAULT_ACTIONS_URL` indicates where the Gitea Actions runners should find the actions with relative path.
 For example, `uses: actions/checkout@v3` means `https://github.com/actions/checkout@v3` since the value of `DEFAULT_ACTIONS_URL` is `github`.