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/ChillDocStoreBundle/Resources/views/AccompanyingCourseDocument/delete.html.twig

@@ -9,11 +9,6 @@
         <dt>{{ 'Title'|trans }}</dt>
         <dd>{{ document.title }}</dd>
 
-        {% if document.scope is not null %}
-            <dt>{{ 'Scope' | trans }}</dt>
-            <dd>{{ document.scope.name | localize_translatable_string }}</dd>
-        {% endif %}
-
         <dt>{{ 'Category'|trans }}</dt>
         <dd>{{ document.category.name|localize_translatable_string }}</dd>
 

src/Bundle/ChillDocStoreBundle/Resources/views/List/list_item.html.twig

@@ -5,18 +5,25 @@
 <div class="item-bloc">
     <div class="item-row">
         <div class="item-col" style="width: unset">
+            {% if document.object.isPending %}
+                <div class="badge text-bg-info" data-docgen-is-pending="{{ document.object.id }}">{{ 'docgen.Doc generation is pending'|trans }}</div>
+            {% elseif document.object.isFailure %}
+                <div class="badge text-bg-warning">{{ 'docgen.Doc generation failed'|trans }}</div>
+            {% endif %}
             <div class="denomination h2">
                 {{ document.title }}
             </div>
-            <div>
-                {{ mm.mimeIcon(document.object.type) }}
-            </div>
+            {% if document.object.type is not empty %}
+                <div>
+                    {{ mm.mimeIcon(document.object.type) }}
+                </div>
+            {% endif %}
             <div>
                 <p>{{ document.category.name|localize_translatable_string }}</p>
             </div>
-            {% if document.template is not null %}
+            {% if document.object.hasTemplate %}
                 <div>
-                    <p>{{ document.template.name.fr }}</p>
+                    <p>{{ document.object.template.name|localize_translatable_string }}</p>
                 </div>
             {% endif %}
         </div>