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/design-system/ui/src/components/radio-group/radio-group.tsx

@@ -110,14 +110,14 @@ const ChoiceBox = React.forwardRef<
       <div className="flex flex-col items-start">
         <Label
           htmlFor={id}
-          size="base"
+          size="small"
           weight="plus"
           className="group-disabled:text-ui-fg-disabled cursor-pointer group-disabled:cursor-not-allowed"
         >
           {label}
         </Label>
         <Hint
-          className="txt-compact-medium text-ui-fg-subtle group-disabled:text-ui-fg-disabled"
+          className="txt-compact-medium text-ui-fg-subtle group-disabled:text-ui-fg-disabled text-left"
           id={descriptionId}
         >
           {description}