[POC] Use the Section VO instead of a custom entity

> Proof of concept

Feeds the Section form with the Section Value Object instead of using a custom object.

Requirements aren't respected, but the existing @require annotations could be replaced with the ones from Form. A next step would be to have 2 distinct forms for Create and Update,
so that they can have their own ValueObject.

Tested manually from `/pjax/section/create`. It works :-)
Better :

```php
$sectionCreateStruct = $this->sectionService->newSectionCreateStruct();
```