[Fleet] Add UI tests for Integration Policy upgrades with conflicts

[joshdover]

See #121436 for tracking of all Fleet UI tests and for guidance on how to structure and write Cypress tests.

Basic coverage for editing an integration (the description field) was added in #121628
Unit tests for validation and saving were added in #125068

We need to have additional coverage that exercises some of the more complex aspects of the policy editor. This is scoped to:

• Integration policy upgrades - this involves more complex interactions with the backend. We have existing coverage of the happy path, need to handle the 'conflict' scenario.
  • When there are conflicts, the user should see a warning callout
  • Form should not save without fixing conflicts

We should use a test package defined in the Kibana repository and served via the local EPR docker container for this type of testing rather than using a real package that will change between releases. We are tracking tests for the specific custom UIs separately, such as #123399

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[juliaElastic]

I've added unit tests for many of these scenarios here: #125068
I'm not sure we need cypress tests as well, since the form validation/submit button is UI only functionality.

[joshdover]

@juliaElastic Thanks I forgot to look at the coverage available there. I've scoped this down to focus on package policy upgrades which are more complex. I think the other coverage we've added in the past few weeks covers the other scenarios well.

[criamico]

@juliaElastic do you know if we already have a dockerized package registry running in Cypress? If not we'll have to create the basic setup needed to write these tests.

[juliaElastic]

@criamico we are not using dockerized package registry with Cypress, you can force install earlier versions of packages to test conflicts.
I'm not sure if we want to use a docker registry or keep using the actual snapshot registry, maybe we should discuss #121436 (comment)

[criamico]

Thanks Julia, I think it's worth exploring the different options. I'll check the other discussion.

[joshdover]

@criamico Instead of using a dockerized EPR, could we explore using the upload package API for this use case? We're already discussing getting rid of the EPR docker image in #128522