envoy_log: allows Envoy version embedding

[mathetake]

Commit Message: envoy_log: allows Envoy version embedding
Additional Description:
We are running multiple Envoy versions on a same VM instance sometimes, so the Envoy's application logs are sometimes interleaved with different Envoy versions, which made it a little bit harder for us to debug later.

This commit adds a new 'E' specifier in the application log to bundle the envoy version in the log line.

Risk Level: low (new code path)
Testing: done
Docs Changes: done
Release Notes: done
Platform Specific Features: n/a

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Caused by: #44337 was opened by mathetake.

see: more, trace.