Add a 'Post User Creation' auth hook (or 'After User Creation')

Problem The Before User Created Auth hook is great when wanting full control of which users are created and which properties created users are going to have. However, they have a significant issue: it's impossible to insert data into the database that is directly linked to the user being created. The problem is straightforward: since the user hasn't been created yet, any foreign key integrity check will fail because there's no user entity to link to. Proposal Add another auth hook, which is triggered once the user is inserted into the database and which is awaited before returning successfully to supabase.auth.signup(). That way, developers can set up the user's account properly on the backend side, and once the user is actually signed in on the frontend, everything is ready to use. The Post User Creation or After User Creation auth hook Example usage A new user is created, and now I have to seed a variety of tables in the database to initialize …