Add USE_SERVICE_WORKER setting (#9110)

* Add USE_SERVICE_WORKER setting

This will be very useful setting for anyone doing frontend work.

Fixes: https://github.com/go-gitea/gitea/issues/9044

* prevent potential syntax error on old browsers

modules/templates/helper.go

@@ -148,6 +148,9 @@ func NewFuncMap() []template.FuncMap {
 		"MetaKeywords": func() string {
 			return setting.UI.Meta.Keywords
 		},
+		"UseServiceWorker": func() bool {
+			return setting.UI.UseServiceWorker
+		},
 		"FilenameIsImage": func(filename string) bool {
 			mimeType := mime.TypeByExtension(filepath.Ext(filename))
 			return strings.HasPrefix(mimeType, "image/")