feat: Add APIs for custom attribute definitions (#2689)

spec/factories/custom_attribute_definitions.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+FactoryBot.define do
+  factory :custom_attribute_definition do
+    sequence(:attribute_display_name) { |n| "Custom Attribute Definition #{n}" }
+    sequence(:attribute_key) { |n| "custom_attribute_#{n}" }
+    attribute_display_type { 1 }
+    attribute_model { 0 }
+    default_value { nil }
+    account
+  end
+end