Add unique constraint for `auth_provider_id` in `users` and `groups` tables

Currently, the `auth_provider_id` field in both the `users` and `groups` tables is not enforced as unique. This can lead to duplicate entries being associated with the same authentication provider, which may cause conflicts or unexpected behavior.

* Update the database schema to add a unique constraint for the `auth_provider_id` field in both the `users` and `groups` tables.