feat: GitHub SSO

[pjhul]

This PR adds to ability to login/signup with GitHub, as well as pretty much overhauling the entire authentication logic.

Changes

• Adds the /api/auth/github route for logging in with GitHub
• Removes the JWT strategy from Passport
• Stores the organization_id in the current session
• Adds more checks for whether a user has admin privileges
• Changes the session cookie name (This is to prevent any stale and incompatible session tokens being used)
• Deletes the refresh_tokens table as it was unused
• Creates the auth providers table
• Removes various other unused fields

Future

• [ ] Add the ability to login with GitHub from the Q&A widget
• [ ] Allow users to connect GitHub to their existing account