Add alarm notifier for case with gnocchi backend

Alarm notifier should be used for storing events in
order to aodh event alarm can work

Change-Id: I0d4d994632b6d74534ea625215667b6658646f34
Related-Prod: https://mirantis.jira.com/browse/PROD-20813
diff --git a/ceilometer/server/backend/gnocchi.yml b/ceilometer/server/backend/gnocchi.yml
index 9eca73b..e93eeaa 100644
--- a/ceilometer/server/backend/gnocchi.yml
+++ b/ceilometer/server/backend/gnocchi.yml
@@ -17,3 +17,7 @@
           # filter_project is deprecated since queens
           filter_project: ${_param:ceilometer_gnocchi_filter_project}
           create_resources: ${_param:ceilometer_create_gnocchi_resources}
+        event_alarm_notifier:
+          enabled: true
+          url: "notifier://?topic=${_param:openstack_event_alarm_topic}"
+          publish_event: true