add websocket group unsubscribe reply

* This change adds more than just an unsubscribe reply.
* Websockets canrequest to join/leave groups. They do so using a single
idempotent request. This change replies to group requests over the
websockets with the diff of the group subscription. i.e. what groups the
user currenntly is in, what groups were left, and what groups were
joined.

awx/main/consumers.py

@@ -204,6 +204,11 @@ class EventConsumer(AsyncJsonWebsocketConsumer):
                 )
             logger.debug(f"Channel {self.channel_name} left groups {old_groups} and joined {new_groups_exclusive}")
             self.scope['session']['groups'] = new_groups
+            await self.send_json({
+                "groups_current": list(new_groups),
+                "groups_left": list(old_groups),
+                "groups_joined": list(new_groups_exclusive)
+            })
 
     async def internal_message(self, event):
         await self.send(event['text'])