Collect hub prometheus metrics
Collect hub prometheus metrics

JupyterHub v1 put them behind auth. Our prometheus
servers don't have access to this auth, so they
can't collect these metrics.

We don't leak usernames or anything like that here, so it'
fine to expose these

ryanlovett/datahub,berkeley-dsep-infra/datahub,berkeley-dsep-infra/datahub,berkeley-dsep-infra/datahub,ryanlovett/datahub,ryanlovett/datahub