[Django4.2 upgrade]: Upgrade django-oauth-lib to latest 2.x.x version

Description

• A PR (link) was created in which we're unpinning django-oauth-toolket and oauthlib.
• The oauthlib has been updated successfully but for django-oauth-toolkit we faced some brokers. And we could only upgrade django-oauth-toolkit to the latest 1.x.x version.
• Our aim is to upgrade it to the latest 2.x.x version.

Blocker

• The main blocker, we faced that in version 2.0.0, django-oauth-toolkit is saving the client-secret as a hashed value instead of plain text.
  https://django-oauth-toolkit.readthedocs.io/en/latest/changelog.html#id12:~:text=%231093%20(Breaking,before%20hitting%20Save
• If we do any attempt to migrate DOT to 2.x.x, it will update all the existing client secrets as well.
• And then we can't downgrade its version. It's only one way.

raise IrreversibleError("Operation %s in %s is not reversible" % (operation, self))
django.db.migrations.exceptions.IrreversibleError: Operation <RunPython <function forwards_func at 0x7f6956652430>> in oauth2_provider.0006_alter_application_client_secret is not reversible

Start with PR 32631 and the django-oauth-toolkit 2.0.0 changelog, then inspect oauth2_provider migration 0006_alter_application_client_secret referenced in the issue. Trace how existing client secrets are stored and how the migration affects them. Done means the project can use the latest 2.x version with an agreed migration path for existing secrets and its irreversible downgrade behavior.