Add onConnect to mqtt and doucment

docs/docs/integrations/mqtt.md

@@ -147,6 +147,10 @@ Message published for each changed review item. The first message is published w
 
 Same data available at `/api/stats` published at a configurable interval.
 
+### `frigate/camera_activity`
+
+Returns data about each camera, its current features, and if it is detecting motion, objects, etc. Can be triggered by publising to `frigate/onConnect`
+
 ### `frigate/notifications/set`
 
 Topic to turn notifications on and off. Expected values are `ON` and `OFF`.

frigate/comms/mqtt.py

@@ -222,6 +222,10 @@ class MqttClient(Communicator):  # type: ignore[misc]
                 self.on_mqtt_command,
             )
 
+        self.client.message_callback_add(
+            f"{self.mqtt_config.topic_prefix}/onConnect", self.on_mqtt_command
+        )
+
         self.client.message_callback_add(
             f"{self.mqtt_config.topic_prefix}/restart", self.on_mqtt_command
         )