Consider using Prometheus for new metrics

[vpavlin]

Prometheus is de facto standard in telemetry, so it would make sense to consider using it to collect our metrics on the client side (go-waku/status-go).

It is also possible to "snapshot" or read current values of the metrics - this would mean we can have metrics locally available via /metrics endpoint if we wanted, but also read and process them and push them to telemetry server in telemetry client.

This would be especially useful for metrics that need to be collected on go-waku (or lower) level as we could just record them there to prometheus and then read them in status-go without any crazy abstractions and leaking or passing custom clients around.

Eventually we could/should also consider pushing metrics to Prometheus PushGateway instead of our custom telemetry server implementation, but that is a stretch goal.