Enrich handshake to allow to return node version (like 8.9.4 or 9.0.0) and commit hash

[amesgen]

Motivation

In order to estimate the rollout of a particular node version (which eg includes a certain bug fix), it would be convenient to query this information from nodes in the network (think SPO relays).

Additionally, this allows users delegating to an SPO to check whether they have already upgraded to a particular node version (assuming they trust them enough to at least not misreport this version).

Any such mechanism can be faked, so it should only be used for informational purposes, or together with an estimation of how many nodes are honest.

Implementation

Guarded behind a new NodeToNodeVersion (experimental at first), the handshake miniprotocol should be enriched to allow to return the node version (a three component version like 8.9.4 or 9.0.0)) and the git hash. These will have to be passed down from the node.