feat(OAuth): Migrate state & code swap to backend

[dvjsharma]

Description

This PR migrates the code and state swap logic to the backend and removes the frontend dependency for the same.

How to test

• Add the FRONTEND_REDIRECT_URL value in the .env file. The server will redirect to this URL with an access token in the query param.
• Get the authorization_url with redirect URL as {domain}/api/v1/live/google-oauth2/callback/.
• Navigate to this URL and sign in using your google account.
• You will be redirected to the forntend URL along with an access token for that user in the query param.

Signed by Divij Sharma