[DESIGN][Enhancement][Elastic Agent] Write down Elastic Agent status report structure

[BenB196]

Describe the enhancement:

When an application/integration is in a CONFIGURING status, the overall health of the agent should be in a CONFIGURING status.

Describe a specific use case for the enhancement or feature:

Currently (tested on 7.17.0), if an application is in the CONFIGURING status, then the overall status of the Agent is HEALTHY

/usr/share/elastic-agent# elastic-agent status
Status: HEALTHY
Message: (no message)
Applications:
  * filebeat               (CONFIGURING)
                           Updating configuration
  * heartbeat              (CONFIGURING)
                           Updating configuration
  * filebeat_monitoring    (HEALTHY)
                           Running
  * metricbeat_monitoring  (HEALTHY)
                           Running

It would be nice, that instead, the over status of the Agent showed as CONFIGURING as well.

Use Case

It would be nice to know when the agent is in a "healthy" state but has not fully transitioned to an actual healthy state.

There are a few reasons why an application could be on a CONFIGURING status, but one interesting one, is if you are using a standalone agent deployment, depending on how badly you mess up the configuring, an application could get stuck in a CONFIGURING status because it can't properly load a new configuration. Since the overall agent health doesn't reflect this status, if you are only checking the overall health, you would never notice this issue unless you're looking for it.

[elasticmachine]

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

[ph]

Actual work in #100 will close this one.