Prometheus compatible metrics endpoint

[mehiel]

First of all, coming from a jvm/spring world for APIs this is exactly what we were looking for.

But what about making the /metrics endpoint prometheus compatible or even introduce a new one. Looking at the prom-client package for an easy step in as well.

Let me know if you'd be interested in something like that.

[JackCuthbert]

Hey @mehiel, that's a great idea! I'm not familiar with what a prometheus metrics endpoint should look like but I'm definitely open to supporting it. Were you looking to open a PR?