Elastic Agent should log the FQDN of the configured Fleet Server on startup

[strawgate]

On startup, the Elastic Agent logs if it believes it's managed by Fleet. Unfortunately, it does not print the name/FQDN of the parent fleet server.

It would be nice if the Elastic Agent log included the Fleet Server that Agent is connected to (or is configured to connect to) on startup.

[elasticmachine]

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