add: DefaultController

* add up method for connection checking

src/Controller/System/DefaultController.php

@@ -39,6 +39,19 @@ class DefaultController extends AbstractController
         $this->navLinks = NavList::LIST;
     }
 
+    #[Route('/up', name: 'app_up')]
+    public function up(): Response
+    {
+        $cnx = $this->entityManager->getConnection();
+        $cnx->connect();
+        $connected = $cnx->isConnected();
+        if ($connected) {
+            return $this->json(true, Response::HTTP_OK);
+        } else {
+            return $this->json(false, Response::HTTP_SERVICE_UNAVAILABLE);
+        }
+    }
+
     #[Route('/dashboard', name: 'app_dashboard')]
     public function dashboard(Request $request, #[CurrentUser()] ?User $user): Response
     {