fix: move coursegraph celery tasks to cms (from lms), and on a non-default, non-high-priority queue.

This is so that the lms default celery queue does not get backed up
when coursegraph is hosed (which is likely when coursegraph has been
redeployed and needs to get the full set of courses).

TNL-8386

cms/envs/common.py

@@ -1389,7 +1389,7 @@ CELERY_DEFAULT_ROUTING_KEY = DEFAULT_PRIORITY_QUEUE
 CELERY_QUEUES = {
     HIGH_PRIORITY_QUEUE: {},
     DEFAULT_PRIORITY_QUEUE: {},
-    LOW_PRIORITY_QUEUE: {}
+    LOW_PRIORITY_QUEUE: {},
 }
 
 # Queues configuration