[Fleet] "Upgrade integration" shown when editing APM package policy

[hop-dev]

Kibana version: 7.16, 8.0, 8.1

Description of the problem including expected versus actual behavior:

Incorrect version of the package policy editor is shown when editing the APM package policy.

Steps to reproduce:

1. Install the APM integration and add it to an agent policy
2. Select edit integration from the agent policy view
3. Notice the package policy editor shows the upgrade layout instead of the edit layout.

Kapture.2021-12-16.at.16.36.31.mp4

[elasticmachine]

Pinging @elastic/fleet (Team:Fleet)

[joshdover]

This is intentional and specific to custom editor UIs that opt in to this behavior: #114914

The point of this feature was to simplify custom editor UI implementations by allowing them to only have to support the schema for their latest package policy. This is acceptable for these editors because these packages are always upgraded on Kibana upgrade but the package policies are not always upgraded. When a user edits one of these packages we force them into upgrading the policy as well to simplify the testing matrix.

Feel free to re-open if I'm misunderstanding!

[hop-dev]

Ah you're right @joshdover, though looks like Kyle did identify further work here which is covered by this issue: #115638 Still correct to close this bug 👍