Make Dashboard's UI locale list dynamic, similar to partnerplatform to allow automatic translations and listing

dashboard

make dashboard own UI locale list dynamic

The change makes Google site verification work reliably. Google's verifier now receives the prerendered page containing the tag, and the tag is set once instead of repeatedly.

partnerplatform

Google site verification meta tag

The old VideoForm and LivestreamForm were only reachable through a hidden `legacyEdit=true` query param on `/content/videos/:id` and `/content/livestreams/:id`. This removes that mode and deletes everything that was only reachable through it.

Changelog.

Remove legacy VideoForm and LivestreamForm and the legacyEdit mode