User permissions are too open

[jcoresongres]

Bug report

Describe the bug

The permissions are too open. The supabase_admin user is a superuser and can do pretty much everything to the database.

When we're using an approach where the schema can be initialized by a superuser, there should be no need to have more permissions after the schema has been created (here by a script).

This should be restricted to an exhaustive list of permissions and what's required on Supabase's side. It should also be defined more clearly which users/roles are required from Supabase's side during runtime.