This function makes it so a buy one gets one free (BOGO) reward will be triggered any time multiple items belonging to the same Line Item Selector are present on a receipt.
E.g., the Major Group "Burgers" may include Burger A, Burger B, and Burger C. If any combination of two of those burgers is present on the receipt, the discount will be given (to the lowest priced item). This is a singular discount, meaning it will only be awarded once per receipt.
