feat: MailJet list handling with DOI, webhook receiver and API endpoint

addresses #869cut134

src/Controller/Api/PickupController.php

@@ -19,7 +19,7 @@ use Symfony\Component\Security\Http\Attribute\IsGranted;
 #[IsGranted('ROLE_OAUTH2_API')]
 class PickupController extends AbstractController
 {
-    private const PLANNING_FILE = 'pickup_planning.json';
+    private const string PLANNING_FILE = 'pickup_planning.json';
 
     public function __construct(
         private readonly PickupLoader $xmlLoader,