[8.x](backport #42041) [system/cpu,core] - Disable performance counter by default to unblock agent CI

[mergify]

Alternative to #42042.

This is a temporary fix as CI on elastic-agent's main is broken https://buildkite.com/elastic/elastic-agent-extended-testing/builds/5390#0193c17f-c655-422a-8dc9-ae5a7a40fdbd.

This most likely happened because user not having enough permissions to read from performance counter. I'll do some more digging and fix the underlying issue.

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This is an automatic backport of pull request #42041 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of f3a063f has failed:

On branch mergify/bp/8.x/pr-42041
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit f3a063f1d.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   metricbeat/docs/modules/system.asciidoc
	both modified:   metricbeat/metricbeat.reference.yml
	both modified:   metricbeat/module/system/_meta/config.reference.yml
	both modified:   metricbeat/module/system/core/_meta/docs.asciidoc
	both modified:   metricbeat/module/system/core/config.go
	both modified:   metricbeat/module/system/cpu/_meta/docs.asciidoc
	both modified:   metricbeat/module/system/cpu/config.go
	both modified:   x-pack/metricbeat/metricbeat.reference.yml

no changes added to commit (use "git add" and/or "git commit -a")

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[botelastic]

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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 mergify/bp/8.x/pr-42041 upstream/mergify/bp/8.x/pr-42041
git merge upstream/8.x
git push upstream mergify/bp/8.x/pr-42041