Improved the functionality of the BP action "Apply a discount to the process depending on the contact groups"

Previously, when creating an order and adding a product, the action "Apply discount to process depending on contact groups" made a check that the customer belongs to one of the selected groups. If it is a member of one of them, then the percentage discounts of the groups are summed up and recorded in the process discount. When moving through the stages and adding 1 more product, the action overlapped. Improved so that when going through the stages and adding 1 more product, the action works only for 1 added product, but not for the previous ones (since they can have a correct price and discount, they can no longer be touched).