Use affix settings with settings validators instead of group settings for monitoring SSL/TLS settings

[danhermann]

The SSL settings should be individual affix settings to facilitate validation both at node startup time and when changed dynamically. Once completed, the affix settings with their respective validators should replace the validators added in #49196. See #49196 (comment) for more context.

[elasticmachine]

Pinging @elastic/es-core-infra (:Core/Infra/Settings)

[elasticmachine]

Pinging @elastic/es-core-features (:Core/Features/Monitoring)

[danhermann]

Our current thinking is that the planned changes to monitoring will eliminate the HTTP exporter and these settings with it. As such, we do not plan to change these settings before the exporter is removed.