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/ChillPersonBundle/Service/DocGenerator/AccompanyingPeriodWorkEvaluationContext.php

@@ -174,6 +174,18 @@ class AccompanyingPeriodWorkEvaluationContext implements
             ->hasPublicForm($template, $entity->getAccompanyingPeriodWork());
     }
 
+    public function contextGenerationDataNormalize(DocGeneratorTemplate $template, $entity, array $data): array
+    {
+        return $this->accompanyingPeriodWorkContext
+            ->contextGenerationDataNormalize($template, $entity, $data);
+    }
+
+    public function contextGenerationDataDenormalize(DocGeneratorTemplate $template, $entity, array $data): array
+    {
+        return $this->accompanyingPeriodWorkContext
+            ->contextGenerationDataDenormalize($template, $entity, $data);
+    }
+
     public function storeGenerated(DocGeneratorTemplate $template, StoredObject $storedObject, object $entity, array $contextGenerationData): void
     {
         $doc = new AccompanyingPeriodWorkEvaluationDocument();