[8.x](backport #5648) [testing/integration]: fix TestLogIngestionFleetManaged

[mergify]

Looking at diagnostics of #5631 failure, it was clear that the monitoring units were not healthy. This is a known issue and it takes some time for them to be healthy.

This PR aims to fix that by making sure the components are healthy before proceeding with the test case.

• Closes [Flaky Test]: TestLogIngestionFleetManaged – Condition never satisfied #5631

  ---

  This is an automatic backport of pull request [testing/integration]: fix TestLogIngestionFleetManaged #5648 done by Mergify.

[mergify]

Cherry-pick of 26f3d59 has failed:

On branch mergify/bp/8.x/pr-5648
Your branch is up to date with 'origin/8.x'.

You are currently cherry-picking commit 26f3d5975e.
  (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:
	modified:   NOTICE.txt
	modified:   testing/integration/logs_ingestion_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   go.mod
	both modified:   go.sum

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

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[elastic-sonarqube]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarQube