[8.16](backport #6085) Fix audit/unenroll calls when agent runs fleet-server

[mergify]

What does this PR do?

Call audit/unenroll (during uninstall) before components are stopped if the elastic-agent is running a fleet-server instance.

Why is it important?

Agents running fleet-server instances would always get an error because fleet-server would be stopped by the time the notify call is attempted.

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

How to test this PR locally

Enroll an agent in a policy with the fleet-server integration and uninstall the agent

Related issues

• Closes elastic-agent installed as Fleet server remains stuck in uninstalling with retry errors for over 4-5 minutes. #5752

  ---

  This is an automatic backport of pull request Fix audit/unenroll calls when agent runs fleet-server #6085 done by Mergify.

[mergify]

Cherry-pick of f321d8a has failed:

On branch mergify/bp/8.16/pr-6085
Your branch is up to date with 'origin/8.16'.

You are currently cherry-picking commit f321d8a72.
  (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/1732043830-Fix-audit-unenroll-call-when-running-fleet-server.yaml
	modified:   internal/pkg/agent/install/uninstall_test.go
	modified:   internal/pkg/fleetapi/ack_cmd.go
	modified:   internal/pkg/fleetapi/audit_unenroll_cmd.go
	modified:   internal/pkg/fleetapi/checkin_cmd.go
	modified:   testing/integration/fleetserver_test.go
	modified:   testing/integration/install_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   internal/pkg/agent/install/uninstall.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

[mergify]

This pull request has not been merged yet. Could you please review and merge it @michel-laterman? 🙏

[elastic-sonarqube]

Quality Gate failed

Failed conditions
3.1% Coverage on New Code (required ≥ 40%)

See analysis details on SonarQube