Fix: Add nubbins for celery monitoring. (#4273)

This commit adds two Celery client configurables necessary for
monitoring.

- CELERY_TASK_TRACK_STARTED
- CELERY_TASK_SEND_SENT_EVENT

For: mitodl/ol-infrastructure#2290

Author: feoh

open_discussions/settings_celery.py

@@ -103,3 +103,6 @@
 CELERY_RESULT_SERIALIZER = "json"
 CELERY_ACCEPT_CONTENT = ["json"]
 CELERY_TIMEZONE = "UTC"
+
+CELEY_TASK_TRACK_STARTED = True
+CELERY_TASK_SEND_SENT_EVENT = True