[BD-14] Migrate all environments to use database-backed organizations (#25153)

* Install `organizations` app into LMS and Studio non-optionally.
* Add toggle `ORGANIZATIONS_AUTOCREATE` to Studio.
* Remove the `FEATURES["ORGANIZATIONS_APP"]` toggle.
* Use the new `organizations.api.ensure_organization` function to
  either validate or get-or-create organizations, depending
  on the value of `ORGANIZATIONS_AUTOCREATE`,
  when creating course runs and V2 content libraries.
  We'll soon use it for V1 content libraries as well.
* Remove the `util.organizations_helpers` wrapper layer
  that had to exist because `organizations` was an optional app.
* Add `.get_library_keys()` method to the Split modulestore.
* Add Studio management command for backfilling organizations tables
  (`backfill_orgs_and_org_courses`).

For full details, see
https://github.com/edx/edx-organizations/blob/master/docs/decisions/0001-phase-in-db-backed-organizations-to-all.rst

TNL-7646