Fix missing migration service loading (#333)

config/migrations.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Symfony\Component\DependencyInjection\Loader\Configurator;
+
+use Terminal42\NotificationCenterBundle\Migration\EmailGatewayMigration;
+
+return static function (ContainerConfigurator $container): void {
+    $services = $container->services();
+    $services->defaults()->autoconfigure();
+
+    $services->set(EmailGatewayMigration::class)
+        ->args([
+            service('database_connection'),
+        ])
+    ;
+};

src/DependencyInjection/Terminal42NotificationCenterExtension.php

@@ -42,6 +42,7 @@ public function load(array $configs, ContainerBuilder $container): void
         $loader->load('listeners.php');
         $loader->load('notification_types.php');
         $loader->load('modules.php');
+        $loader->load('migrations.php');
 
         $container->registerForAutoconfiguration(GatewayInterface::class)
             ->addTag(self::GATEWAY_TAG)