[8.14](backport #4961) Introduce agent.monitoring.metrics_period

[mergify]

What does this PR do?

This PR introduces agent.monitoring.metrics_period field

Why is it important?

I consider this PR important as it allows each user to control the sampling period of monitoring metrics according to them needs

Checklist

• My code follows the style guidelines of this project
  - [ ] I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool
  - [ ] I have added an integration test or an E2E test

Disruptive User Impact

None

How to test this PR locally

Spawn an agent with setting the config agent.monitoring.metrics_period

Related issues

• Closes https://github.com/elastic/ingest-dev/issues/2680

---

This is an automatic backport of pull request #4961 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 6a45256 has failed:

On branch mergify/bp/8.14/pr-4961
Your branch is up to date with 'origin/8.14'.

You are currently cherry-picking commit 6a452564dd.
  (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)

Changes to be committed:
	new file:   changelog/fragments/1718818524-support-monitoring-metrics-interval.yaml
	modified:   internal/pkg/agent/application/coordinator/diagnostics_test.go
	modified:   internal/pkg/core/monitoring/config/config.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   _meta/config/common.p2.yml.tmpl
	both modified:   _meta/config/common.reference.p2.yml.tmpl
	both modified:   _meta/config/elastic-agent.docker.yml.tmpl
	both modified:   elastic-agent.docker.yml
	both modified:   elastic-agent.reference.yml
	both modified:   elastic-agent.yml
	both modified:   internal/pkg/agent/application/monitoring/v1_monitor.go
	both modified:   internal/pkg/agent/application/monitoring/v1_monitor_test.go

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

[pierrehilbert]

It looks like some changes are depending on #4586
@cmacknz Do we really want to continue to backport this taking this new information into account?

[pierrehilbert]

Looks like we can ignore my message and that @pkoutsovasilis did the necessary adjustments.

[elastic-sonarqube]

Quality Gate passed

Issues
2 New issues
1 Fixed issue
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube