Add test cases for selected ingest customisation scenarios

[endorama]

With #16267 we are adding a more extensive test coverage to apm-server, testing more in depth version upgrades and ingest functionalities.

What those tests do not include are customization to the default setup provided via the apm-data Elasticsearch plugin. As this is a common scenario for our customers, we could get value in testing some common customization scenarios our customer use.

Goal: add test cases to verify apm-server works as expected in few selected customization scenarios. Scenarios to test have to be identified by analyzing common customization applied by our community and customers.

Impact: Close a blind spot in our automated testing when configurations deviate from the out of the box default we provide.