created base structure of admin page

app/admin/categories/page.tsx

@@ -0,0 +1,11 @@
+import React from "react";
+
+export default function AdminCategoriesPage() {
+  return (
+    <div>
+      <h1>Page to manage categories</h1>
+      <a href="/admin/categories/create">create new category</a> <br />
+      <p>List of existing category</p>
+    </div>
+  );
+}