fix: don't send emails on library backup/restore

There is no way to resume either the backup or restore library actions,
i.e. if you navigate away from it, you have to do it again. This is a
limitation of the current UI because we wanted to get something quick
and simple in for Ulmo, but it also reflects the fact that library
backup/restore should be much faster than course import/export has
historically been.

In any case, sending an email for a 5-10 second task is unnecessary and
distracting, so this commit suppresses the email.

Note: I'm using local imports to get around the fact that the
content_libraries public API is used by content_libraries/tasks.py
which defines the tasks. I can't import from content_libraries/tasks.py
directly, because that would violate import linter rules forbidding
other apps from importing things outside of api.py. This isn't ideal,
but it keeps the fix small and it keeps the logic in the
content_libraries app.

cms/djangoapps/cms_user_tasks/signals.py

@@ -12,6 +12,7 @@ from user_tasks.signals import user_task_stopped
 
 from cms.djangoapps.contentstore.toggles import bypass_olx_failure_enabled
 from cms.djangoapps.contentstore.utils import course_import_olx_validation_is_enabled
+from openedx.core.djangoapps.content_libraries.api import is_library_backup_task, is_library_restore_task
 
 from .tasks import send_task_complete_email
 
@@ -64,6 +65,28 @@ def user_task_stopped_handler(sender, **kwargs):  # pylint: disable=unused-argum
         if olx_artifact and not bypass_olx_failure_enabled():
             return olx_artifact.text
 
+    def should_skip_end_of_task_email(task_name) -> bool:
+        """
+        Studio tasks generally send an email when finished, but not always.
+
+        Some tasks can last many minutes, e.g. course import/export. For these
+        tasks, there is a high chance that the user has navigated away and will
+        want to check back in later. Yet email notification is unnecessary and
+        distracting for things like the Library restore task, which is
+        relatively quick and cannot be resumed (i.e. if you navigate away, you
+        have to upload again).
+
+        The task_name passed in will be lowercase.
+        """
+        # We currently have to pattern match on the name to differentiate
+        # between tasks. A better long term solution would be to add a separate
+        # task type identifier field to Django User Tasks.
+        return (
+            is_library_content_update(task_name) or
+            is_library_backup_task(task_name) or
+            is_library_restore_task(task_name)
+        )
+
     status = kwargs['status']
 
     # Only send email when the entire task is complete, should only send when
@@ -72,7 +95,7 @@ def user_task_stopped_handler(sender, **kwargs):  # pylint: disable=unused-argum
         task_name = status.name.lower()
 
         # Also suppress emails on library content XBlock updates (too much like spam)
-        if is_library_content_update(task_name):
+        if should_skip_end_of_task_email(task_name):
             LOGGER.info(f"Suppressing end-of-task email on task {task_name}")
             return