EA Diagnostics - Env var is no more available

[lucabelluccini]

In recent versions of EA, the diagnostics do not contain the Environment Variables defined on the host.
The file variables.yaml doesn't contain the env vars anymore.

• 8.17.0 -> present
• 8.18.0 -> missing
• 8.19.5 -> missing
• 9.1.5 -> missing

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)