Promteheus metric for tezos node version info

[jevonearth]

Similar to the well known prometheus metric go_build_info

We would like a tezos_build_info metric that interrogates the Tezos RPC /version endpoint.

The tezos_build_info communicates the version and buildinfo of the Tezos node that the tezos_exporter is scraping. If the node that is being scraped is updated, the labels for tezos_build_info will update accordingly.

This feature gives visibility from the monitoring perspective about what Tezos (octez) node versions are running.

See: https://tezos.gitlab.io/shell/rpc.html#get-version