Extend docs about deployment of zone CPs in multi-zone setup with "Universal on k8s"

[schogges]

Description

xref: #2083 (comment)

In the docs about CP deployment in multi-zone setup we have included documentation about "Universal on Kubernetes" in the section about the global CP.
In the lower parts we have only included documentation about k8s and universal.

Should we extend the documentation in the section about Set up the zone control planes with "Universal on Kubernetes"?

[lukidzi]

Triage: we should add docs and probably check if it works

[github-actions]

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