[Elastic Agent] Expose httpprof for Elastic Agent

[ruflin]

Beats can be run with the --httpprof flag to expose an http server for profiling. For debugging purpose, this should also be supported by Elastic Agent.

If Elastic Agent is started with --httpprof, how will this affect the sub processes? What about the ones written in a different language? How can a subprocess like metricbeat be profiled?

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[jlind23]

@ruflin shouldn't we close this one and rather use: elastic/elastic-agent#107?

[ruflin]

I think this issue can be closed with the recent work that @michel-laterman was doing related pprof.