Feature Request - Prometheus/OpenMetrics endpoint

[neufeldtech]

It would be great to have a Prometheus or OpenMetrics endpoint in the HTTP api (/metrics) to be able to gain visibility on how much data is passing through a particular proxy.

A Common question that often comes up when using Toxiproxy in complex environments (with automation, in Kubernetes) is "is my data actually flowing through Toxiproxy?". Having a standard metrics endpoint could help solve that.

Exposing these in a common metric format (Prometheus/OpenMetrics) rather than a custom format (arbitrary JSON or other) would enable wide adoption by folks that already have infrastructure deployed for ingesting Prometheus-style metrics.

For history, see also #266 where metrics were originally proposed (but through a custom format).