Adds API to fetch all legacy library content blocks that are ready to be updated to use library v2 and convert to item banks.
Also adds API to update all the references via a user celery task and to fetch its status.
BREAKING CHANGE: All references to the hardcoded 'proctortrack' string have
been removed from the codebase, as well as the `studio.show_review_rules`
waffle flag. These were used to determine whether an escalation email is
required and whether review rules should be shown. These decisions are now made
based on the value of 'requires_escalation_email' (default False) and 'show_review_rules'
(default True) config items in the PROCTORING_BACKENDS entry.
Additionally:
* The proctoring info api will now return the list of providers which require an escalation
email so that frontend-app-learning does not need to use a hardcoded check agaist
the provider name 'proctortrack'.
* Removed translation commands, mock variables and user facing strings that contained
'proctortrack'.
* Updated all test cases that were using proctortrack to use fake providers names.
Part of: https://github.com/openedx/edx-platform/issues/36329
