fix: Rename some tasks to match new import paths (#26236)

Several tasks are explicitly named as (or like)
their old, deprecated import path.

The issue here is that django-user-tasks listens for task
invocations, and attempts to import the task based on its name.
If the task name is completely wrong, user-tasks will catch
the ImportError and move on.
If the task is a valid *deprecated* import, though, then
user-tasks will choke on the raised `DeprecatedEdxPlatformImportError`.

Thus, we must rename three tasks to their new full path:
1. entitlements.expire_old_enrollments
2. third_party_auth.fetch_saml_metadata
3. student.send_activation_email

The first two are run daily, and so are safe to be
renamed in place.

The third task must be renamed using an expand-contract
pattern; otherwise, we would drop hundreds of tasks
during the App vs. Worker out-of-sync version window
that happens at deployments.
This commit is the expand phase.

common/djangoapps/entitlements/tasks.py

@@ -19,11 +19,7 @@ LOGGER = get_task_logger(__name__)
 MAX_RETRIES = 11
 
 
-@shared_task(
-    bind=True,
-    ignore_result=True,
-    name='entitlements.expire_old_entitlements',
-)
+@shared_task(bind=True, ignore_result=True)
 @set_code_owner_attribute
 def expire_old_entitlements(self, start, end, logid='...'):
     """

common/djangoapps/student/tasks.py

@@ -20,9 +20,13 @@ from openedx.core.lib.celery.task_utils import emulate_http_request
 log = logging.getLogger('edx.celery.task')
 
 
-@shared_task(bind=True, name='student.send_activation_email')
+# This is a task function that is in the process of being renamed.
+# In order to avoid dropping tasks during deployment, we have to register it twice,
+# once under each name. This allows us to cut from one name to the other safely.
+# Once we have fully switched to the new name, we can go back to registering
+# this task function with a simple decorator.
 @set_code_owner_attribute
-def send_activation_email(self, msg_string, from_address=None):
+def _send_activation_email(self, msg_string, from_address=None):
     """
     Sending an activation email to the user.
     """
@@ -67,3 +71,15 @@ def send_activation_email(self, msg_string, from_address=None):
             dest_addr,
         )
         raise Exception
+
+
+_OLD_TASK_NAME = 'student.send_activation_email'
+_NEW_TASK_NAME = 'common.djangoapps.student.tasks.send_activation_email'
+
+
+# Register task under both its old and new names,
+# but expose only the old-named task for invocation.
+# -> Next step: Once we deploy and teach Celery workers the new name,
+#    set `send_activation_email` to the new-named task.
+send_activation_email = shared_task(bind=True, name=_OLD_TASK_NAME)(_send_activation_email)
+shared_task(bind=True, name=_NEW_TASK_NAME)(_send_activation_email)

common/djangoapps/third_party_auth/tasks.py

@@ -31,7 +31,7 @@ class MetadataParseError(Exception):
     pass
 
 
-@shared_task(name='third_party_auth.fetch_saml_metadata')
+@shared_task
 @set_code_owner_attribute
 def fetch_saml_metadata():
     """