feat(admin-sdk,admin-bundler,admin-shared,medusa): Restructure admin packages (#8988)

**What**
- Renames /admin-next -> /admin
- Renames @medusajs/admin-sdk -> @medusajs/admin-bundler
- Creates a new package called @medusajs/admin-sdk that will hold all tooling relevant to creating admin extensions. This is currently `defineRouteConfig` and `defineWidgetConfig`, but will eventually also export methods for adding custom fields, register translation, etc. 
  - cc: @shahednasser we should update the examples in the docs so these functions are imported from `@medusajs/admin-sdk`. People will also need to install the package in their project, as it's no longer a transient dependency.
  - cc: @olivermrbl we might want to publish a changelog when this is merged, as it is a breaking change, and will require people to import the `defineXConfig` from the new package instead of `@medusajs/admin-shared`.
- Updates CODEOWNERS so /admin packages does not require a review from the UI team.

packages/admin/dashboard/src/components/authentication/protected-route/index.ts

@@ -0,0 +1 @@
+export * from "./protected-route"

packages/admin/dashboard/src/components/authentication/protected-route/protected-route.tsx

@@ -0,0 +1,30 @@
+import { Spinner } from "@medusajs/icons"
+import { Navigate, Outlet, useLocation } from "react-router-dom"
+import { useMe } from "../../../hooks/api/users"
+import { SearchProvider } from "../../../providers/search-provider"
+import { SidebarProvider } from "../../../providers/sidebar-provider"
+
+export const ProtectedRoute = () => {
+  const { user, isLoading } = useMe()
+  const location = useLocation()
+
+  if (isLoading) {
+    return (
+      <div className="flex min-h-screen items-center justify-center">
+        <Spinner className="text-ui-fg-interactive animate-spin" />
+      </div>
+    )
+  }
+
+  if (!user) {
+    return <Navigate to="/login" state={{ from: location }} replace />
+  }
+
+  return (
+    <SidebarProvider>
+      <SearchProvider>
+        <Outlet />
+      </SearchProvider>
+    </SidebarProvider>
+  )
+}