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/src/lib/format-provider.ts

@@ -0,0 +1,12 @@
+/**
+ * Providers only have an ID to identify them. This function formats the ID
+ * into a human-readable string.
+ * @param id - The ID of the provider
+ * @returns A formatted string
+ */
+export const formatProvider = (id: string) => {
+  return id
+    .split("-")
+    .map((s) => s.charAt(0).toUpperCase() + s.slice(1))
+    .join(" ")
+}