[Fleet] Assess and stub-out tests for Policy-Action change in 7.10 cycle

[EricDavisX]

see this comment for details: https://github.com/elastic/kibana/pull/81236#issuecomment-713181915

We can probably best use the e2e-testing framework for this need. One task is to re-evaluate how the relating change needs to be tested and ensure we have coverage for it (we have some in this repo already of course!), but it is possible we still have more holes (even after manual regression) because this came up late in the cycle

@nchaulet can you give a review over the changes to start us off? or we can schedule a meeting to review.