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.go

@@ -1775,5 +1775,7 @@ func (a *App) CountNotificationReason(
 		a.Metrics().IncrementNotificationErrorCounter(notificationType, notificationReason)
 	case model.NotificationStatusNotSent:
 		a.Metrics().IncrementNotificationNotSentCounter(notificationType, notificationReason)
+	case model.NotificationStatusUnsupported:
+		a.Metrics().IncrementNotificationUnsupportedCounter(notificationType, notificationReason)
 	}
 }