Send an email when a workflow is send to an external

- create an event subscriber to catch the workflow which arrive to a "sentExternal" step;
- add a messenger's message to handle the generation of the email;
- add a simple message, and a simple controller for viewing the document
- add dedicated tests

src/Bundle/ChillMainBundle/Controller/WorkflowViewSendPublicController.php

@@ -0,0 +1,25 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace Chill\MainBundle\Controller;
+
+use Chill\MainBundle\Entity\Workflow\EntityWorkflowSend;
+use Symfony\Component\HttpFoundation\Response;
+use Symfony\Component\Routing\Annotation\Route;
+
+class WorkflowViewSendPublicController
+{
+    #[Route('/public/main/workflow/send/{uuid}/view/{verificationKey}', methods: ['GET'], name: 'chill_main_workflow_send_view_public')]
+    public function __invoke(EntityWorkflowSend $workflowSend, string $verificationKey): Response
+    {
+        return new Response('ok');
+    }
+}