Make version management easy

[dawsontoth]

Fabric configuration that's currently edited manually through the API/DB has no UI — e.g. which Harper versions are published, and per-org version scoping (central-manager#580). Routine changes like exposing a version for one org's upgrade need an engineer to add and later remove entries by hand (Slack thread).

Build an admin-only section in studio to view and edit these configuration tables.

• Visible to fabric admins only.
• First table: available Harper versions, global and per-org (pairs with Logs Page Refactor #580).
• Enumerate the remaining configuration tables when picking this up — the ask was a UI around all of them.