Feature Request: Support Prometheus / Openmetrics

[Tuxdude]

It would be great to get a /metrics endpoint (or an alternative endpoint if /<something> always means the user something) to allow the opengist job to be monitored using Prometheus or other metrics collector that supports the Openmetrics format.

Even if we can expose just an up metric to begin with, that would be a great start to probe the health of through Prometheus. Other metrics to export can be decided and added subsequently.