chore: add deprecation comment to commonLabels

[stormqueen1990]

commonLabels is deprecated, but the field did not have a deprecation comment, like other fields do. Add the deprecation comment, as some IDEs use that as a guideline to show a strikethrough in the field names (and to follow the pattern of other deprecated fields).

/kind documentation

[koba1t]

I think the commonLabels is already deprecated with the PR below.
#5464

Thanks @stormqueen1990
/lgtm
/approve

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[koba1t]

Hi @stormqueen1990
Could you add a deprecated message for web docs?
https://github.com/kubernetes-sigs/cli-experimental/blob/master/site/content/en/references/kustomize/kustomization/commonlabels/_index.md

[stormqueen1990]

Hi @stormqueen1990 Could you add a deprecated message for web docs? https://github.com/kubernetes-sigs/cli-experimental/blob/master/site/content/en/references/kustomize/kustomization/commonlabels/_index.md

Hi there, @koba1t! Sure thing!