[APM Server] Support Elastic Agent Conditions

[BenB196]

Request

It would be nice to have the ability to control when APM Server runs via https://www.elastic.co/guide/en/fleet/current/dynamic-input-configuration.html

Use Case

If I am running Elastic Agent on Kubernetes as a Daemonset across all nodes, and I want to deploy APM Server as highly available on this Daemonset, there are some cases, where I might not want APM Server to run on all nodes. Example, if I have both "generic" and "specific" nodes that the Daemonset runs on ("generic" might have different resources available CPU/RAM/Disk), I want to be able to limit the APM server to only run on the "specific" nodes and I could leverage this via conditions.