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/einterfaces/metrics.go

@@ -101,4 +101,5 @@ type MetricsInterface interface {
 	IncrementNotificationSuccessCounter(notificationType model.NotificationType)
 	IncrementNotificationErrorCounter(notificationType model.NotificationType, errorReason model.NotificationReason)
 	IncrementNotificationNotSentCounter(notificationType model.NotificationType, notSentReason model.NotificationReason)
+	IncrementNotificationUnsupportedCounter(notificationType model.NotificationType, notSentReason model.NotificationReason)
 }