Based on best practices: https://prometheus.io/docs/practices/naming/#metric-names

Suggestion: Prefix all metrics with beaconchain_.

It'll be very nice for all the client implementations to converge on a set of metrics for support. The benefits of metrics standardization includes enabling of converged monitoring across difference implementations, better debugging support in multi client testnet, and better instrumentations which can lead to more client side optimizations.
At the minimal, we should converge on the naming first, and the set of baseline metrics to implement second. There will be divergences such a language dependent metrics and that is ok. (eg. goroutines for Golang, JVM thread counts of JAVA... etc)

It's useful to have slot vs. head_slot, and in a similar way, it's useful to have epoch vs. finalized, justified, previous_justified.

I think we should add epoch to the standard list of metrics...

By default, the Prometheus collection endpoint should be served from 0.0.0.0:8008.

Avoid a whole set of HTTP server vulnerabilities by listening only on localhost by default.

Based on best practices: https://prometheus.io/docs/practices/naming/#metric-names

Suggestion: Add unit to some metrics.

• reorg_events_total (total because it's a counter)