fix(kuma-cp): mistakenly setting 'kuma.io/display-name' as label (backport of #10430)

[kumahq]

Automatic cherry-pick of #10430 for branch release-2.9

Generated by action

cherry-picked commit da824ce
⚠️ ⚠️ ⚠️ Conflicts happened when cherry-picking! ⚠️ ⚠️ ⚠️

On branch release-2.9
Your branch is up to date with 'origin/release-2.9'.

You are currently cherry-picking commit da824ce57.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   pkg/plugins/runtime/k8s/webhooks/defaulter.go
	both modified:   pkg/plugins/runtime/k8s/webhooks/defaulter_test.go

no changes added to commit (use "git add" and/or "git commit -a")