feat(graphql): add error codes to graphql errors

spec/controllers/api/v2/graphql_controller_spec.rb

@@ -684,7 +684,7 @@ describe API::V2::GraphqlController do
           end
 
           it "should return an error" do
-            expect(gql_errors).to eq([{ message: "Cannot return null for non-nullable field PersonneMorale.siegeSocial" }])
+            expect(gql_errors).to eq([{ message: "Cannot return null for non-nullable field PersonneMorale.siegeSocial", extensions: { code: "invalid_null" } }])
           end
         end
       end