add broadcast websocket metrics

* Gather brroadcast websocket metrics and push them into redis every
configurable seconds.
* Pop metrics from redis in web view layer to display via the api on
demand

awx/main/management/commands/run_wsbroadcast.py

@@ -23,5 +23,3 @@ class Command(BaseCommand):
             loop.run_until_complete(task)
         except KeyboardInterrupt:
             logger.debug('Terminating Websocket Broadcaster')
-            if broadcast_websocket_mgr:
-                broadcast_websocket_mgr.stop()