Add validation for subscription steps

app/Http/Controllers/SubscriptionStepsController.php

@@ -1,16 +1,25 @@
 <?php
 
+/**
+ * Invoice Ninja (https://invoiceninja.com).
+ *
+ * @link https://github.com/invoiceninja/invoiceninja source repository
+ *
+ * @copyright Copyright (c) 2022. Invoice Ninja LLC (https://invoiceninja.com)
+ *
+ * @license https://www.elastic.co/licensing/elastic-license
+ */
+
 namespace App\Http\Controllers;
 
 use App\Livewire\BillingPortal\Purchase;
+use App\Rules\Subscriptions\Steps;
 use Illuminate\Http\JsonResponse;
 
 class SubscriptionStepsController extends BaseController
 {
     public function index(): JsonResponse
     {
-        // @todo: perhaps integrate this in statics
-
         $dependencies = collect(Purchase::$dependencies)
             ->map(fn($dependency) => [
                 'id' => $dependency['id'],
@@ -22,4 +31,13 @@ class SubscriptionStepsController extends BaseController
 
         return response()->json($dependencies);
     }
+
+    public function check(): JsonResponse
+    {
+        request()->validate(([
+            'steps' => ['required', new Steps()]
+        ]));
+
+        return response()->json([], 200);
+    }
 }