Feature: [docgen] generate documents in an async queue

The documents are now generated in a queue, using symfony messenger. This queue should be configured:

```yaml
# app/config/messenger.yaml
framework:
    messenger:
        # reset services after consuming messages
        # reset_on_message: true

        failure_transport: failed

        transports:
            # https://symfony.com/doc/current/messenger.html#transport-configuration
            async: '%env(MESSENGER_TRANSPORT_DSN)%'
            priority:
                dsn: '%env(MESSENGER_TRANSPORT_DSN)%'
            failed: 'doctrine://default?queue_name=failed'

        routing:
            # ... other messages
            'Chill\DocGeneratorBundle\Service\Messenger\RequestGenerationMessage': priority
```

`StoredObject`s now have additionnal properties:

* status (pending, failure, ready (by default) ), which explain if the document is generated;
* a generationTrialCounter, which is incremented on each generation trial, which prevent each generation more than 5 times;

The generator computation is moved from the `DocGenTemplateController` to a `Generator` (implementing `GeneratorInterface`. 

There are new methods to `Context` which allow to normalize/denormalize context data to/from a messenger's `Message`.

src/Bundle/ChillDocGeneratorBundle/Service/Generator/GeneratorInterface.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Chill\DocGeneratorBundle\Service\Generator;
+
+use Chill\DocGeneratorBundle\Entity\DocGeneratorTemplate;
+use Chill\DocStoreBundle\Entity\StoredObject;
+use Symfony\Component\HttpFoundation\File\File;
+
+interface GeneratorInterface
+{
+    /**
+     * @template T of File|null
+     * @template B of bool
+     * @param B $isTest
+     * @param (B is true ? T : null) $testFile
+     * @psalm-return (B is true ? string : null)
+     * @throws \Symfony\Component\Serializer\Exception\ExceptionInterface|\Throwable
+     */
+    public function generateDocFromTemplate(
+        DocGeneratorTemplate $template,
+        int                  $entityId,
+        array                $contextGenerationDataNormalized,
+        ?StoredObject        $destinationStoredObject = null,
+        bool                 $isTest = false,
+        ?File                $testFile = null
+    ): ?string;
+}