[Monitoring] Add tests for logic around waiting for usage collectors

[chrisronline]

From #36153, we introduced logic to wait for collectors, but we had issues getting this working for tests so we introduced configuration that removes the logic that causes the collectors to wait. This works fine for the PR, but we should add some tests, somewhere, that will capture and test this waiting scenario.

Per this comment, we might want to add this to https://github.com/elastic/elastic-stack-testing

[elasticmachine]

Pinging @elastic/stack-monitoring