Notification metrics fixes (#26854)

* Ensure your own posts are never ACKed

* Don't ACK mobile websocket notifications

* Add counter for the unsupported Desktop Apps

* Count only push messages when checking for acks

* Fix generated

* Add tests, fix comment

* Fix help string

* Check for nil session

server/channels/app/notification_push.go

@@ -185,6 +185,10 @@ func (a *App) sendPushNotificationToAllSessions(msg *model.PushNotification, use
 		if a.Metrics() != nil {
 			a.Metrics().IncrementPostSentPush()
 		}
+
+		if msg.Type == model.PushTypeMessage {
+			a.CountNotification(model.NotificationTypePush)
+		}
 	}
 
 	return nil