feat(dashboard): Regions domain (#6534)

**What**
- Implements new Region domain design
- Adds new SplitView component for managing adding nested relations in FocusModals, eg. adding countries to a region.
- Adds new Combobox component for multi select fields in forms

**medusajs/ui**
- Fix styling of RadioGroup.Choicebox component

CLOSES CORE-1650, CORE-1671

packages/admin-next/dashboard/tailwind.config.cjs

@@ -24,5 +24,5 @@ module.exports = {
   theme: {
     extend: {},
   },
-  plugins: [require("@headlessui/tailwindcss")],
+  plugins: [],
 }