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/Entity/StoredObject.php

@@ -41,12 +41,6 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
 
     use TrackCreationTrait;
 
-    /**
-     * @ORM\Column(type="datetime", name="creation_date")
-     * @Serializer\Groups({"read", "write"})
-     */
-    private DateTimeInterface $creationDate;
-
     /**
      * @ORM\Column(type="json", name="datas")
      * @Serializer\Groups({"read", "write"})
@@ -87,7 +81,7 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
     private string $title = '';
 
     /**
-     * @ORM\Column(type="text", name="type")
+     * @ORM\Column(type="text", name="type", options={"default": ""})
      * @Serializer\Groups({"read", "write"})
      */
     private string $type = '';
@@ -105,9 +99,20 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
 
     /**
      * @ORM\Column(type="text", options={"default": "ready"})
+     * @Serializer\Groups({"read"})
      */
     private string $status;
 
+    /**
+     * Store the number of times a generation has been tryied for this StoredObject.
+     *
+     * This is a workaround, as generation consume lot of memory, and out-of-memory errors
+     * are not handled by messenger.
+     *
+     * @ORM\Column(type="integer", options={"default": 0})
+     */
+    private int $generationTrialsCounter = 0;
+
     /**
      * @param StoredObject::STATUS_* $status
      */
@@ -117,8 +122,16 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
         $this->status = $status;
     }
 
+    public function addGenerationTrial(): self
+    {
+        $this->generationTrialsCounter++;
+
+        return $this;
+    }
+
     /**
      * @Serializer\Groups({"read", "write"})
+     * @deprecated
      */
     public function getCreationDate(): DateTime
     {
@@ -135,6 +148,11 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
         return $this->filename;
     }
 
+    public function getGenerationTrialsCounter(): int
+    {
+        return $this->generationTrialsCounter;
+    }
+
     public function getId(): ?int
     {
         return $this->id;
@@ -158,6 +176,9 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
         return $this->getFilename();
     }
 
+    /**
+     * @return StoredObject::STATUS_*
+     */
     public function getStatus(): string
     {
         return $this->status;
@@ -185,6 +206,7 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
 
     /**
      * @Serializer\Groups({"write"})
+     * @deprecated
      */
     public function setCreationDate(DateTime $creationDate): self
     {
@@ -244,4 +266,30 @@ class StoredObject implements AsyncFileInterface, Document, TrackCreationInterfa
 
         return $this;
     }
+
+    public function getTemplate(): ?DocGeneratorTemplate
+    {
+        return $this->template;
+    }
+
+    public function hasTemplate(): bool
+    {
+        return null !== $this->template;
+    }
+
+    public function setTemplate(?DocGeneratorTemplate $template): StoredObject
+    {
+        $this->template = $template;
+        return $this;
+    }
+
+    public function isPending(): bool
+    {
+        return self::STATUS_PENDING === $this->getStatus();
+    }
+
+    public function isFailure(): bool
+    {
+        return self::STATUS_FAILURE === $this->getStatus();
+    }
 }