Add notification policies and notification requests (#29366)

spec/fabricators/notification_request_fabricator.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+Fabricator(:notification_request) do
+  account
+  from_account { Fabricate.build(:account) }
+  last_status { Fabricate.build(:status) }
+  dismissed false
+end