Github Oauth scope

Currently the scope used for Github oauth is defined manually:
https://github.com/dwyl/auth/blob/e1216674c478d5fcb983f0c2f919829a50db1ca2/lib/auth_web/controllers/auth_controller.ex#L65

However with our [Labels application](https://github.com/dwyl/labels/) we want to allow users to login with Github and to be able to add/remove labels from repositories. This means that we need a way for the auth app to define which scopes to allow for the applications.

List of Github scopes: https://docs.github.com/en/developers/apps/building-oauth-apps/scopes-for-oauth-apps