Describe the enhancement:
Enhance Beats CI to call new e2e Agent test when Elastic Agent files change

• Automation Team was kind enough to help us set up a small initial test for Agent! The next step is to have it run when Agent files change.
  Files from this repo location should trigger the noted CI:
  https://github.com/elastic/beats/tree/master/x-pack/elastic-agent

The e2e test is here:
https://github.com/elastic/e2e-testing/tree/master/e2e/_suites/ingest-manager

It can be called as, from the elastic/e2e-testing repo e2e/_suites/ingest-manager
$ godog -t stand_alone_mode

• you'll also need dependencies of course. specifics are being Doc'ed for that immediately so we can use them here.

Note, this project is in use for Metricbeat already.

Question for @ruflin @ph @michalpristas - should we also run this separate test when Metricbeat or Filebeat changes are put in to ensure nothing from those repos breaks Elastic Agent downstream?
Meaning, changes to these locations will trigger the Ingest Manager / Agent e2e test as well:

• https://github.com/elastic/beats/tree/master/filebeat
• https://github.com/elastic/beats/tree/master/metricbeat

Describe a specific use case for the enhancement or feature:
Lets say a developer somehow puts a bug into the code, during PR CI this could catch it so it isn't merged, which saves the company time overall.