This totally removes the following N+1 query from the GET /shops request
```sql
SELECT "spree_properties".* FROM "spree_properties"
INNER JOIN "spree_product_properties"
ON "spree_product_properties"."property_id" = "spree_properties"."id"
INNER JOIN "spree_products"
ON "spree_products"."id" = "spree_product_properties"."product_id"
INNER JOIN "enterprises"
ON "enterprises"."id" = "spree_products"."supplier_id"
WHERE "spree_products"."supplier_id" = 24;
```
The product properties of the corresponding enterprises are now loaded
in a single query fired from the controller.
