[MM-57066][MM-57329] Added metrics for all notification stopping points, consolidated categories between metrics and logging (#26799)

* [MM-57066] Add metric counters for notification events

* Some small changes

* Account for Metrics() sometimes being nil

* Fix test (again)

* Fix more tests

* A few changes from testing - added success counter

* Missed a mock

* Lint

* Add feature flag for notification monitoring

server/channels/app/web_broadcast_hooks_test.go

@@ -87,7 +87,8 @@ func TestPostedAckHook_Process(t *testing.T) {
 	hook := &postedAckBroadcastHook{}
 	userID := model.NewId()
 	webConn := &platform.WebConn{
-		UserId: userID,
+		UserId:   userID,
+		Platform: &platform.PlatformService{},
 	}
 
 	t.Run("should ack if user is in the list of users to notify", func(t *testing.T) {