Draft: Add new binary tezos-metrics

This MR is the continuation of the project https://gitlab.com/nomadic-labs/tezos-metrics .

Tezos-metrics implements an openmetrics server to feed databased like prometheus.

It uses the tezos-libraries for encoding/decoding json messages for all the shell components and had-hoc decoders for protocol-specific metrics.

it is currently used for development, it is important to use a version of tezos-metrics specifically compiled for each development branch.

I move the project inside the tezos code base to make it easy to integrate the deployment of tezos metrics with the rest of the node.

documentation page : https://nomadic-labs.gitlab.io/-/tezos/-/jobs/1509404663/artifacts/docs/_build/developer/metrics.html?highlight=metrics

(if the page is not available, replace 1509404663 with the number of the latest job that produces documentation. cf. https://gitlab.com/nomadic-labs/tezos/-/pipelines/354422771 Job is named documentation:build-passed)