fix(kuma-cp): deep copy tags when gen. outbounds (backport #5070)

[mergify]

This is an automatic backport of pull request #5070 done by Mergify.
Cherry-pick of 81ccca0 has failed:

On branch mergify/bp/release-1.8/pr-5070
Your branch is up to date with 'origin/release-1.8'.

You are currently cherry-picking commit 81ccca0f6.
  (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)

Changes to be committed:
	modified:   pkg/xds/sync/proxy_builder_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   pkg/xds/topology/outbound.go

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[bartsmykla]

lgtm