Enable API support for primary taxon

Allows access to the newly added attribute through existing product APIs.

Author: JustShah

api/lib/spree/api_configuration.rb

@@ -7,7 +7,7 @@ class ApiConfiguration < Preferences::Configuration
     preference :product_attributes, :array, default: [
       :id, :name, :description, :available_on,
       :slug, :meta_description, :meta_keywords, :shipping_category_id,
-      :taxon_ids, :total_on_hand, :meta_title
+      :taxon_ids, :total_on_hand, :meta_title, :primary_taxon_id
     ]
 
     preference :product_property_attributes, :array, default: [:id, :product_id, :property_id, :value, :property_name]

api/spec/requests/spree/api/products_spec.rb

@@ -316,6 +316,13 @@ module Spree::Api
           expect(json_response["taxon_ids"]).to eq([taxon_1.id])
         end
 
+        it "puts primary taxon for the product" do
+          product_data[:primary_taxon_id] = taxon_1.id.to_s
+          post spree.api_products_path, params: { product: product_data }
+
+          expect(json_response["primary_taxon_id"]).to eq(taxon_1.id)
+        end
+
         # Regression test for https://github.com/spree/spree/issues/4123
         it "puts the created product in the given taxons" do
           product_data[:taxon_ids] = [taxon_1.id, taxon_2.id].join(',')
@@ -404,6 +411,13 @@ module Spree::Api
           expect(json_response["taxon_ids"]).to eq([taxon_1.id])
         end
 
+        it "puts primary taxon for the updated product" do
+          product.primary_taxon_id = taxon_2.id
+          put spree.api_product_path(product), params: { product: { primary_taxon_id: taxon_1.id } }
+
+          expect(json_response["primary_taxon_id"]).to eq(taxon_1.id)
+        end
+
         # Regression test for https://github.com/spree/spree/issues/4123
         it "puts the created product in the given taxons" do
           put spree.api_product_path(product), params: { product: { taxon_ids: [taxon_1.id, taxon_2.id].join(',') } }