[18.0][ADD] sale_customer_order_frequency

[petrus-v]

Compute customer order frequency statistics:

• Average order duration: Average number of days between confirmed orders.
• Days since last order: Number of days elapsed since the last confirmed order.
• Days until next order: Estimated number of days until the next order based on the average

[luisDIXMIT]

Code review and LGTM!