Add test notification tool (#28334)

* Add test notification tool

* Add frontend styles

* Remove option from admin view

* Refactor create post and add translations

* Fix several CI errors

* Fix API and frontend snapshots

* Refactor trailing and leading icon on buttons

* Add different button states

* i18n-extract

* Fix wrong text

* Add tests

* Fix wrong string

* Fix test

* feat: E2E send test notifications (#28371)

* Refactor send desktop notification

* Address rest of the feedback

* Fix tests

* Add correct link

* Fix test

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: yasserfaraazkhan <attitude3cena.yf@gmail.com>

server/channels/api4/system.go

@@ -45,6 +45,7 @@ func (api *API) InitSystem() {
 	api.BaseRoutes.System.Handle("/timezones", api.APISessionRequired(getSupportedTimezones)).Methods(http.MethodGet)
 
 	api.BaseRoutes.APIRoot.Handle("/audits", api.APISessionRequired(getAudits)).Methods(http.MethodGet)
+	api.BaseRoutes.APIRoot.Handle("/notifications/test", api.APISessionRequired(testNotifications)).Methods(http.MethodPost)
 	api.BaseRoutes.APIRoot.Handle("/email/test", api.APISessionRequired(testEmail)).Methods(http.MethodPost)
 	api.BaseRoutes.APIRoot.Handle("/site_url/test", api.APISessionRequired(testSiteURL)).Methods(http.MethodPost)
 	api.BaseRoutes.APIRoot.Handle("/file/s3_test", api.APISessionRequired(testS3)).Methods(http.MethodPost)
@@ -232,6 +233,16 @@ func getSystemPing(c *Context, w http.ResponseWriter, r *http.Request) {
 	}
 }
 
+func testNotifications(c *Context, w http.ResponseWriter, r *http.Request) {
+	_, err := c.App.SendTestMessage(c.AppContext, c.AppContext.Session().UserId)
+	if err != nil {
+		c.Err = err
+		return
+	}
+
+	ReturnStatusOK(w)
+}
+
 func testEmail(c *Context, w http.ResponseWriter, r *http.Request) {
 	var cfg *model.Config
 	err := json.NewDecoder(r.Body).Decode(&cfg)