Update variant name instead of product via DFC

A DFC SuppliedProduct relates to a Spree::Variant and when updating its
name we only want to change the name for that variant. Otherwise, when
we update the name of the product, it would update the name for all
variants and all the corresponding SuppliedProducts.

engines/dfc_provider/app/services/supplied_product_builder.rb

@@ -49,10 +49,10 @@ class SuppliedProductBuilder < DfcBuilder
 
   def self.apply(supplied_product, variant)
     variant.product.assign_attributes(
-      name: supplied_product.name,
       description: supplied_product.description,
     )
 
+    variant.display_name = supplied_product.name
     QuantitativeValueBuilder.apply(supplied_product.quantity, variant.product)
     variant.unit_value = variant.product.unit_value
   end

engines/dfc_provider/spec/requests/supplied_products_spec.rb

@@ -188,7 +188,7 @@ describe "SuppliedProducts", type: :request, swagger_doc: "dfc.yaml", rswag_auto
             submit_request(example.metadata)
             variant.reload
           }.to change { variant.description }.to("DFC-Pesto updated")
-            .and change { variant.name }.to("Pesto novo")
+            .and change { variant.display_name }.to("Pesto novo")
             .and change { variant.unit_value }.to(17)
         end
       end

swagger/dfc.yaml

@@ -489,7 +489,7 @@ paths:
                     "@context": https://www.datafoodconsortium.org
                     "@id": http://test.host/api/dfc/enterprises/10000/supplied_products/10001
                     "@type": dfc-b:SuppliedProduct
-                    dfc-b:name: Apple - 6g
+                    dfc-b:name: Apple (6g)
                     dfc-b:description: A delicious heritage apple
                     dfc-b:hasType: dfc-pt:non-local-vegetable
                     dfc-b:hasQuantity: