Broken/Flaky integration tests on main

[pchila]

After the last few merges on main we got a few integration tests failures:

https://buildkite.com/elastic/elastic-agent/builds/3663#018af41b-d3b7-43fb-972b-b72472513600

• TestAPMConfig
  It seems that APM config is not correctly propagated to components anymore: in the test the component tries to use the default parameters attempting to connect to APM server on http://localhost:8200/intake/v2/events
  Update: it seems that in the latest 8.11.0-SNAPSHOT elastic cloud version the APM server endpoint returns 502/503 HTTP error. Testing against 8.10.2 makes the test pass. Opened Fix apm test #3504 to set 8.10.2 version for apm integration test until the issue is solved.
• TestStandaloneDowngradeToSpecificSnapshotBuild
  This test seems trying to downgrade on the same snapshot build:

      upgrade_downgrade_test.go:86: 
        	Error Trace:	/home/ubuntu/agent/testing/integration/upgrade_downgrade_test.go:86
        	Error:      	Received unexpected error:
        	            	failed to start agent upgrade to version "8.11.0": exit status 1
        	            	Error: Failed trigger upgrade of daemon: TarInstaller: creating file /opt/Elastic/Agent/data/elastic-agent-35dbbd/elastic-agent: open /opt/Elastic/Agent/data/elastic-agent-35dbbd/elastic-agent: text file busy
        	            	For help, please see our troubleshooting guide at https://www.elastic.co/guide/en/fleet/8.11/fleet-troubleshooting.html
        	Test:       	TestStandaloneDowngradeToSpecificSnapshotBuild
  

  this is similar to Flaky test: TestUpgradeBrokenPackageVersion #3454 and we expected to be fixed in Refactor and fix all upgrade integration tests #3477
  Update: this test seems to be just flaky. Will update Flaky test: TestUpgradeBrokenPackageVersion #3454 adding this testcase and further updates will be tracked in the specific issue.
• TestInstallAndUnenrollWithEndpointSecurity/protected
  This was already identified as flaky (twice, tracked by [Meta] Flaky integration tests #3357 and Flaky Test: TestInstallWithEndpointSecurityAndRemoveEndpointIntegration/* #3480)
  Update: this test is also as flaky as tracked in the specific issue, will track further updates there.

[elasticmachine]

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