[Feature Request] - Metrics Reporting

[probably-not]

I started looking at Hitch to use as a SSL/TLS Sidecar for services in K8S. I was able to get HTTPS working for my services, which is awesome. Unfortunately, I'm entirely blind to what's happening within Hitch, since there are no metrics reported anywhere.

It would be great to see metrics of things like the current number of TLS sessions, latencies (for SSL Handshakes and for other things like forwarding the bytes to the backends), any errors that can happen. For example, I saw a few logs here and there that say "Handshake failed" but if I wasn't looking at logs I would have no idea that it happened, which would be a critical issue in a true production system.

Once there's a way for these stats to be reported, exporters for popular metrics solutions such as Prometheus and InfluxDB can be written.