report user activity on the hub

[rfeltstykket]

For good record keeping, we need to find a way to pull all of the active users for the cluster and log it. It looks like this should be possible from the API endpoints /users and /user here:

https://jupyterhub.readthedocs.io/en/0.9.0/_static/rest-api/index.html

after that we can filter it by some window (e.g. 2 weeks) and log it.

[TimStewartJ]

I'm just now looking into this, it seems to be relatively simple to interact with jupyterhub's api. This also made me realize our metrics data with prometheus and grafana hasn't been persistent so I am looking into adding that now.