Implement Leaderboard component, User auth, Database

[Arpit-Khandelwal]

Here's a working demo: https://leaderboard.arpitkhandelwal.com/

Disclamer: Code is scrappy, not very clean or optimized, wanted feedback on a basic v0.

Implemented User auth using Github provider from Next auth
Implemented Database from supabase, (haven't watched Prisma/orm class yet). Storing user and access token for now,
Implemented Backend solely for securing all user's access tokens, when sending req for PR/issues vis github api.
Leaderboard is mostly done by v0.dev, did few changes and refactors

TODO:

• Use octokit for github api calls
• (maybe cron job) fetch and save all user's contribution to DB, then fetch it from Backend, one way to avoid github api rate limit (possible issue when lot of people start using)

@hkirat