feat: add index route

src/Controller/HealthcheckController.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace App\Controller;
+
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Attribute\Route;
+
+class HealthcheckController
+{
+    #[Route('/', name: 'healthcheck')]
+    public function healthcheck(): Response
+    {
+        return new Response("ok");
+    }
+}