[Story] User registration

[halsk]

Goal:

As a project leader, I want to register for the service So that I can manage my projects

Tasks:

1. Add OAuth settings on the supabase (GitHub Auth so far)
2. Add client-side code
3. Check the way to test locally.
4. Update documents

Acceptance Criteria:

• [x] Users can register via GitHub
• [x] Users can sign in
• [x] Users can sign out
• Users can delete their account -> postpone to #12
• [ ] Users can register via Twitter
• [ ] Users can register via Facebook

[halsk]

Let's use password-less authentication so far. When we need to use passwords for authentication, we can implement it later.

[halsk]

Deleting users needs to be considered how we have to handle the projects and activities that the user associated. I created #12, and I skip the implementation of the feature so far.