Add Vue 3 migration FF for geo apps

What does this MR do and why?

Creates vue3_migrate_geo and verifies geo creation, edit and settings pages. The remaining pages will be in a second MR merging into this one !260434 (merged)

Verifies pages work fine with the flag enabled.

References

Geo issue -> #632330 (closed)

Import issue -> #613597 (closed)

Screenshots or screen recordings

What	Page
admin/geo/settings (settings)
Empty state when no geo sites admin/geo/sites
List when sites exist admin/geo/sites
Adding a site /admin/geo/sites/new
Editting existing site admin/geo/sites/1/edit

How to set up and validate locally (Optional)

1. Requires a Premium or Ultimate license

2. Enable feature flag vue3_migrate_geo

3. Geo sites exist at admin/geo/sites

4. You'd need to have a primary site, and can create one in rails console for gdk (verify the url is the correct one for your instance)

   GeoNode.create!(name: "gdk", url: "http://127.0.0.1:3000/", primary: true)

MR acceptance checklist

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