Add platform information for push notification metrics (#27460)

* Add platform information for push notification metrics

* Address feedback

* Add the client platform returned by the devices to the normalize function

* Add "no platform" platform label to distinguish from unknown

server/channels/app/web_broadcast_hooks.go

@@ -139,7 +139,7 @@ func incrementWebsocketCounter(wc *platform.WebConn) {
 		return
 	}
 
-	wc.Platform.Metrics().IncrementNotificationCounter(model.NotificationTypeWebsocket)
+	wc.Platform.Metrics().IncrementNotificationCounter(model.NotificationTypeWebsocket, model.NotificationNoPlatform)
 }
 
 // getTypedArg returns a correctly typed hook argument with the given key, reinterpreting the type using JSON encoding