changes done to /app/api/github/callback/route.ts file to handle expiration

[Yashasv-Prajapati]

Changes done to /app/api/github/callback/route.ts file to handle expiration of access token using refresh token.

1. First it checks if the user access token is valid or not by sending a request to fetch the repositories.
2. If the access token is not valid, then it uses the refresh token stored in db to fetch a new access token and then again make a request for fetching repositories.
3. No more requests are made and gives error and nothing is displayed on the client-side

[linear[bot]]

CS3-95 Github handle access_token expiration

In case the access_token expires(which it does in every 8hours), use the refresh_token stored in db to perform operations on db.