Feature: Support beaconcha.in stats collection

[yorickdowne]

Is your feature request related to a problem? Please describe.
Grandine cannot send stats to beaconcha.in. Grandine users are not able to monitor their node on their beaconcha.in mobile app.

Describe the solution you'd like
Implement metrics push to beaconcha.in natively. The spec is here: https://github.com/gobitfly/eth2-client-metrics

Clients that currently support this collection natively are Lighthouse, Lodestar and Teku.

Describe alternatives you've considered
Teach the eth2-client-metrics-exporter how to get metrics from Grandine

[sauliusgrigaitis]

Did you try --remote-metrics-url https://docs.grandine.io/metrics.html . Some time ago it worked.

[yorickdowne]

Thanks! In fact I am using that already but didn't document that, and forgot I was. Sorry for the noise! And Happy New Year.