fix problem with Kubewarden chart upgrade

[aalves08]

Summary

Fixes #15710

Occurred changes and/or fixed issues

• fix problem with Kubewarden chart upgrade
• update unit test

Technical notes summary

Areas or cases that should be tested

1) Direct usecase for issue (problem upgrading KW chart):

• Add kubewarden repository in local - Apps - Repositories of type http and url https://charts.kubewarden.io
• Go To Apps - Repositories, search for Kubewarden and install the chart
• Verify that kubewarden-controller version 5.7.0 and kubewarden-crds version 1.21.0 are installed
• Go to "Preferences" -> Helm Chart -> "Include Prerelease Versions"
• Go To Apps - Repositories, search for Kubewarden and click to upgrade the chart (should be upgrading to 5.8.0-rc1)
• Verify that upgrade succeeded

2) Test general chart install
3) Test general chart upgrade

Areas which could experience regressions

• installing/upgrading charts

Screenshot/Video

Screen.Recording.2025-10-27.at.13.30.57.mov

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[codyrancher]

I think we should go with your suggestion around adding an extra argument to the diff method to determine if we use the new method.

By doing this it will reduce the risk without complicating much. I don't want to end up with a duplicate method unless we also plan to dig into this further and deprecate it.

I believe this null is related to the fact that there are times if we want to save a resource and delete a field we have to specify that field as null to delete because if it's set to undefined it will do nothing. I don't fully recall where this has occurred though.