add graphql endpoint

app/graphql/mutations/base_mutation.rb

@@ -0,0 +1,9 @@
+# frozen_string_literal: true
+module Mutations
+  class BaseMutation < GraphQL::Schema::RelayClassicMutation
+    argument_class Types::BaseArgument
+    field_class Types::BaseField
+    input_object_class Types::BaseInputObject
+    object_class Types::BaseObject
+  end
+end