[Admin Dashboard] Use Github Apps and Deprecate Admin PATs

[harshkhandeparkar]

The Problem
Currently, both a Github OAuth app and an administrator's PAT (personal access token) is required for checking the user's membership in the admin team. The personal admin token needs to be generated by an admin each time it expires and constantly needs to be changed. It would be better if personal tokens are deprecated entirely.

Possible solutions
Use Github App for the authentication. The access token generated by the Github App can be fine grained and be used for checking the membership without required an admin token.