feat: initial auth backend

[ap0nia]

Features (based on #890)

Correct columns in schema

• id (required) -> user ID / username
• googleId (optional) -> google ID
• userData (required) -> schedule
• visibility (optional) -> visibility

The id column is required and the primary key for identification. The googleId is optional, and populated once the user has logged in with Google OAuth. Users logging in via Google will be checked using the googleId column instead of id column.

Functionality

Loading user data

No visibility checks, just loads the schedule as asked. This may be adjusted to be more like the "viewing" functionality, which isn't currently active on the frontend.

Viewing user data

Assumes a user ID requesting another user ID flow. Checks that the requested schedule is visible.

[ap0nia]

Oops, yeah I forgot about the discussion. Re: #890

[MinhxNguyen7]

Seems about right ¯_(ツ)_/¯

[MinhxNguyen7]

I'm not entirely sure what's going on, and I don't know what the risks are to merging this, so you can merge it in when you feel fit @ap0nia