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

modules/setting/actions.go

@@ -22,9 +22,11 @@ var (
 		ZombieTaskTimeout     time.Duration     `ini:"ZOMBIE_TASK_TIMEOUT"`
 		EndlessTaskTimeout    time.Duration     `ini:"ENDLESS_TASK_TIMEOUT"`
 		AbandonedJobTimeout   time.Duration     `ini:"ABANDONED_JOB_TIMEOUT"`
+		SkipWorkflowStrings   []string          `ìni:"SKIP_WORKFLOW_STRINGS"`
 	}{
-		Enabled:           true,
-		DefaultActionsURL: defaultActionsURLGitHub,
+		Enabled:             true,
+		DefaultActionsURL:   defaultActionsURLGitHub,
+		SkipWorkflowStrings: []string{"[skip ci]", "[ci skip]", "[no ci]", "[skip actions]", "[actions skip]"},
 	}
 )