Upstream OAuthenticator features in use by Earthscope

[yuvipanda]

As part of #3618, we have two features in use by earthscope:

• Modifying the name of the user after authentication so it's valid [All] Make username_claim callable (except for CILogon), like it has been in Generic jupyterhub/oauthenticator#717
• Allowing login only when a specified set of scopes are granted Add allowed_scopes to all authenticators to allow some users based on granted scopes jupyterhub/oauthenticator#719
• Appropriately redirect to hub home page when logged out [Auth0] Allow redirecting to custom URL after logout jupyterhub/oauthenticator#722

This ticket tracks getting both these PRs merged upstream, and then bringing them in so we can remove the custom python code in the earthscopes common.yaml config file

[damianavila]

I am also tracking those ones in the sprint board so we make sure we do not track of them.

[yuvipanda]

two PRs have been meged, and the 3rd has been deemed not necessary! \o/