Add the ability to run on the ESGF JupyterHub (US-side)

[mgrover1]

I think it would be good to enable the Jupyterhub launch to nimbus, the ESGF (US-side of the project) resource.

Currently, we have this in a fork of the repository, but I think it would be better to be within the main version.

[brian-rose]

@mgrover1 can you point us to the relevant fork? This sounds like a cool addition. Also do you feel confident enough to pin a priority label on this one?