DOC-4759 Add a basic tenant operations page

[aimurphy]

• Add a page that summarizes how to create, view, edit, and delete tenants, namespaces, and topics. This is a summary only; it isn't meant as a replacement for more detailed information elsewhere in the docs, especially for the API and CLI options.
• Create a separate Admin section in the nav, and move some topics around. Note: I have another ticket to revisit the API reference section.
• Update Enable georeplication to match the UI

[plpesvc-ds]

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[mendonk]

+1