Update celery routing for celery 4+ (#25567)

* Update celery routing

- Used routing function instead of class
- Move task queues dictionary to Django settings
- Removed routing_key parameter
- Refactored routing for singleton celery instantiation

Co-authored-by: Awais Qureshi <awais.qureshi@arbisoft.com>

common/djangoapps/entitlements/tasks.py

@@ -11,8 +11,7 @@ from edx_django_utils.monitoring import set_code_owner_attribute
 from common.djangoapps.entitlements.models import CourseEntitlement
 
 LOGGER = get_task_logger(__name__)
-# Under cms the following setting is not defined, leading to errors during tests.
-ROUTING_KEY = getattr(settings, 'ENTITLEMENTS_EXPIRATION_ROUTING_KEY', None)
+
 # Maximum number of retries before giving up on awarding credentials.
 # For reference, 11 retries with exponential backoff yields a maximum waiting
 # time of 2047 seconds (about 30 minutes). Setting this to None could yield
@@ -23,7 +22,6 @@ MAX_RETRIES = 11
 @task(
     bind=True,
     ignore_result=True,
-    routing_key=ROUTING_KEY,
     name='entitlements.expire_old_entitlements',
 )
 @set_code_owner_attribute