Add an event subscriber for config export

Closes #3463662

core/modules/package_manager/src/EventSubscriber/ConfigSubscriber.php

+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\package_manager\EventSubscriber;
+
+use Drupal\Core\Config\ConfigEvents;
+use Drupal\Core\Config\StorageTransformEvent;
+use Symfony\Component\EventDispatcher\EventSubscriberInterface;
+
+/**
+ * Event subscriber to remove executable paths from exported config.
+ *
+ * @internal
+ *   This is an internal part of Package Manager and may be changed or removed
+ *   at any time without warning. External code should not interact with this
+ *   class.
+ */
+final class ConfigSubscriber implements EventSubscriberInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getSubscribedEvents(): array {
+    return [
+      ConfigEvents::STORAGE_TRANSFORM_EXPORT => 'onExport',
+    ];
+  }
+
+  /**
+   * Removes executable paths from exported config.
+   *
+   * @param \Drupal\Core\Config\StorageTransformEvent $event
+   *   The event object.
+   */
+  public function onExport(StorageTransformEvent $event): void {
+    $storage = $event->getStorage();
+
+    $settings = $storage->read('package_manager.settings');
+    $settings['executables'] = [
+      'composer' => NULL,
+      'rsync' => NULL,
+    ];
+    $storage->write('package_manager.settings', $settings);
+  }
+
+}