Part of [[ https://linear.app/comm/issue/ENG-4269/implement-the-database-schema | ENG-4269 ]].
Mostly copied logic from `http::handlers::blob::assign_holder_handler` and `http::handlers::blob::remove_holder_handler` - but now with using the new database methods
Partially addresses the [[ https://github.com/CommE2E/comm/blob/9457487cd7f063b994c8bb77bcc5ded8128e795f/services/blob/src/http/handlers/blob.rs#L348 | TODO ]] from `http::handlers::blob::remove_holder_handler` - auto deletion of orphaned blobs can now be disabled
Depends on D8455.