[Notifier] Disable notifications on failed messages by default

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/Configuration.php

@@ -1516,6 +1516,7 @@ class Configuration implements ConfigurationInterface
                             ->prototype('scalar')->end()
                         ->end()
                     ->end()
+                    ->booleanNode('notification_on_failed_messages')->defaultFalse()->end()
                     ->children()
                         ->arrayNode('channel_policy')
                             ->useAttributeAsKey('name')

src/Symfony/Bundle/FrameworkBundle/DependencyInjection/FrameworkExtension.php

@@ -1934,9 +1934,11 @@ class FrameworkExtension extends Extension
             $container->removeDefinition('notifier.channel.email');
         }
 
-        if (!$this->messengerConfigEnabled) {
-            $container->removeDefinition('notifier.failed_message_listener');
-        } else {
+        if ($this->messengerConfigEnabled) {
+            if ($config['notification_on_failed_messages']) {
+                $container->getDefinition('notifier.failed_message_listener')->addTag('kernel.event_subscriber');
+            }
+
             // as we have a bus, the channels don't need the transports
             $container->getDefinition('notifier.channel.chat')->setArgument(0, null);
             $container->getDefinition('notifier.channel.email')->setArgument(0, null);

src/Symfony/Bundle/FrameworkBundle/Resources/config/notifier.xml

@@ -44,7 +44,6 @@
 
         <service id="notifier.failed_message_listener" class="Symfony\Component\Notifier\EventListener\SendFailedMessageToNotifierListener">
             <argument type="service" id="notifier" />
-            <tag name="kernel.event_subscriber" />
         </service>
 
         <!-- chatter -->