add. method to generate query call for user registration date: user_registration_date
add. method to generate query call for user registration date: user_registration_date

rfaulkner/wikipedia_user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/analytics-user-metrics,wikimedia/analytics-user-metrics,wikimedia/user_metrics,rfaulkner/wikipedia_user_metrics,wikimedia/user_metrics,wikimedia/user_metrics,wikimedia/analytics-user-metrics