Many deployments would like a custom proxy version pushed as a stat to stats sinks so that is used along with other stats to compare the behaviours. Current envoy pushes part of SHA server.version stat that is not fully usable if envoy version is wrapped with custom proxy wrappers.

The proposal is to introduce a new proxy_version field in in bootstrap config and when it is set, the server.version should use that value instead of the current value. If there is a value in also sending part of git sha, we can introduce a new stat called server.proxy_version.