[Feature] Start/stop monitoring server based on monitoring config

[michalpristas]

due to cloud scenario where they have disabled monitoring but expect server to be running

this needs to be in sync with fleet to distinguish monitoring.enabled because we don't want to monitor anything and disabled because server should be down

Fixes: #2734

[elasticmachine]

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

[elasticmachine]

Pinging @elastic/elastic-agent (Team:Elastic-Agent)

[elasticmachine]

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• Start Time: 2023-10-30T07:21:31.609+0000

• Duration: 26 min 28 sec

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Name	Metrics % (covered/total)	Diff
Packages	98.837% (85/86)	👍 0.014
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Classes	66.132% (371/561)	👍 0.121
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[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b feat/relax-server upstream/feat/relax-server
git merge upstream/main
git push upstream feat/relax-server

[cmacknz]

I think we need to change the agent configuration used in cloud first, and since we are doing that we should address #2509 which will also need a cloud configuration change.

See #2734 (comment)

[michalpristas]

this is dependent on work defined here: elastic/kibana#168629
kibana/fleet will signal 3 states (enabled, metrics, logs)

• true, true, true: metrics and logs collection enabled
• true, false, false: metrics and logs are not collected but server is running
• false, false, false: metrics and logs are not collected, server is shutdown.

default behavior is either 1st or 3rd with very few exceptions which falls into seconds case.

[michalpristas]

all dependent work is done. bringing this alive

[AndersonQ]

[Suggestion]
You could use an atomic.Bool instead of the mutex. I believe it'd make the code easier to maintain as it's not imediately obvious start() and stop() cannot lock the mutex because Reload() does so and then call them.

[michalpristas]

good point

[michalpristas]

failing on some unrelated tests, some of which are already addressed by @belimawr

[mergify]

This pull request is now in conflicts. Could you fix it? 🙏
To fixup this pull request, you can check out it locally. See documentation: https://help.github.com/articles/checking-out-pull-requests-locally/

git fetch upstream
git checkout -b feat/relax-server upstream/feat/relax-server
git merge upstream/main
git push upstream feat/relax-server

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