add new demo symfony files

app/src/Event/CommentCreatedEvent.php

@@ -0,0 +1,30 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Event;
+
+use App\Entity\Comment;
+use Symfony\Contracts\EventDispatcher\Event;
+
+class CommentCreatedEvent extends Event
+{
+    protected $comment;
+
+    public function __construct(Comment $comment)
+    {
+        $this->comment = $comment;
+    }
+
+    public function getComment(): Comment
+    {
+        return $this->comment;
+    }
+}