* it allows to find related object via URL scope
GET /api/categories/{cat-id}/products
* it allows to find related objects via where filter
GET /api/products?filter[where][categoryId]={cat-id}
(skipped for now)
* it includes requested related models in `find`
GET /api/categories/findOne
?filter[where][id]=CAT-ID&filter[include]=products
* it includes requested related models in `findById`
GET /api/categories/{cat-id}?include=products
(skipped for now)