I am trying to add translations to Sylius' product variant model, but having some trouble configuring the resource.

When dealing with custom models it is easy to add translation classes, just create the necessary classes with the right interfaces and then include them in the resources configuration file, like below:

```
# resources.yml
app.orientation:
            driver: doctrine/orm
            classes:
                model: AppBundle\Entity\Orientation\Orientation
            translation:
                classes:
                    model: AppBundle\Entity\Orientation\OrientationTranslation

```

I have already added the necessary classes to the product variant and customised the product variant itself to make it translatable. The last step is to activate the translation classes (only the model in this case). The problem is that when I try to add the model to my config.yml I get the following error:

> 
> Unrecognized option "translation" under
>  "sylius\_product.resources.product\_variant"
> 
> 
> 

So how am I supposed to enable the translation of the product variant model?

Configuration reference:

```
# config.yml
sylius_product:
    resources:
        product_variant:
            classes:
                factory: AppBundle\Factory\Product\ProductVariantFactory
                model: AppBundle\Entity\Product\ProductVariant
                form:
                    default: AppBundle\Form\Type\Product\ProductVariantType
            translation:
                classes:
                    model: AppBundle\Entity\Product\ProductVariantTranslation

```