What kind of change does this PR introduce?

Bug fix

What is the current behavior?

Docs reference creating extensions with @, e.g. supabase@dbdev, even though those changes haven't been rolled out yet and don't work when run against even a new Supabase project.

What is the new behavior?

Revert back to the old way that still works and is still referenced here: https://database.dev/supabase/dbdev