Allow to configure the Fleet Server internal host

[AndersonQ]

Describe the enhancement:

Allow to configure the Fleet Server host used by the Elastic Agent when bootstrapping Fleet Server

Describe a specific use case for the enhancement or feature:

When using mTLS the Elastic Agent and Fleet Server should be able to use TLS certificate issued to unique names/IPs, without the need to have either certificate issued to localhost

What is the definition of done?

It's possible to bootstrap a Fleet Server using mTLS where neither Fleet Server's certificate nor the Elastic Agent's certificate are issued to localhost

[elasticmachine]

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