add createUser mutation

spec/graphql/inputs/user_attributes_input_spec.rb

@@ -0,0 +1,11 @@
+# frozen_string_literal: true
+require "rails_helper"
+
+RSpec.describe(Inputs::UserAttributesInput) do
+  subject { described_class }
+
+  describe "arguments" do
+    it { is_expected.to(accept_argument(:first_name).of_type("String!")) }
+    it { is_expected.to(accept_argument(:last_name).of_type("String!")) }
+  end
+end