[Fleet, Elastic Agent] Review the SSL/TLS/CA parameters in the Fleet Server & Elastic Agent pages

Right now, we only document the Fleet Server secured setup, but my suggestion would be to create 2 separate pages:

1) How to deploy Fleet Server
2) How to deploy Elastic Agent

In particular, in each page, we need to group up the flags/env vars depending on what is affected:
- Elastic Agent to Fleet Server
- Elastic Agent to Elasticsearch/Logstash/other
- Fleet Server to Elasticsearch

We also need to attempt to provide best practices and info on what can be overridden by the policy vs what can/must be provided via CLI.
We also need to clarify mTLS:
- between EA and FS
- between EA and ES/Logstash/other
- between FS and ES