[Elastic Endpoint / Fleet] Expand Agent host/restart/revoke tests now that Endpoint tests are merged

[EricDavisX]

There are a number of high-priority tests that we should add and run regularly, now that we're able to.

this line of code, for example is a great test:
https://github.com/elastic/e2e-testing/blob/master/e2e/_suites/ingest-manager/features/fleet_mode_agent.feature#L37

• but it doesn't cover Endpoint. And we found a bug recently showing off the problem, so I'm dropping in this ticket to help prioritize the work.

that ticket is here:
elastic/beats#21424

Theoretically we should have *all the building blocks to do this already, and should only need feature file changes, I think!

[EricDavisX]

@IgorGuz2000 setting you as assigned - this has been waiting for Endpoint to be re-activated after the expansion to use real VMs in the test. I'd say you are in a good position to make sure those tests are re-enabled and then you can finish off/re-work this small addition (if still relevant). sound good?