Integrate next-auth with existing functionality

[dongheenam]

We now need to integrate next-auth with the app.

Tasks

• [ ] Redirect \questions to login page if not logged in
• [x] user id in questions
• [x] question bucket management
• [x] user can edit questions locally (to bucket) & globally (to Questions)

[dongheenam]

Progress update

To simplify the logic, buckets are saved in localStorage. They will either be quickly deleted or added to a test anyways.