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

addresses #869cut134

src/Message/MailjetNewsletterEventMessage.php

@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Message;
+
+final class MailjetNewsletterEventMessage
+{
+    public const string EVENT_UNSUBSCRIBE = 'unsub';
+
+    /**
+     * @param array<string, mixed> $payload
+     */
+    public function __construct(
+        public readonly string $email,
+        public readonly int $mailjetListId,
+        public readonly string $event,
+        public readonly ?\DateTimeImmutable $eventAt = null,
+        public readonly array $payload = [],
+    ) {
+    }
+}