Add snapshot test of prometheus metrics

[mhofman]

What is the Problem Being Solved?

We should understand the impact of making changes to our prometheus metrics. While there is various ways to confuse consumers of these, the most obvious one is a change in which metrics are reported. Another is possibly a change in the type or characteristic of the metric

Description of the Design

A snapshot style test, at worse in a3p-integration (but preferably in an ava based required test, like in the cosmic-swingset package), that queries the metrics Prometheus endpoint and snapshots at least the set of metrics exported, and if possible metadata about the characteristics of these metrics.

Security Considerations

None

Scaling Considerations

None

Test Plan

This is a test

Upgrade Considerations

None