Coupon Promotion Discount in Field

When configuring a coupon program, users can now choose the reward type "Discount in Line". This makes the promotion behave like a normal line discount: the percentage is written into the Discount column of the eligible sales order lines, so the discount is visible and editable directly on the order lines rather than appearing as a separate reward product line.

• The program form shows a Discount percentage field when this reward type is selected, and hides the reward product and discount type fields that do not apply.
• Selecting this reward type requires the "Discount on sales order lines" setting to be enabled; otherwise Odoo raises an error asking the user to enable it.
• The discount can apply to the whole order, to the cheapest product, or to specific products, following the program's existing applicability settings.
• When a coupon code for such a program is applied, the discount is set on the matching order lines and the program is stored on the order.
• The order count and the "Sales Orders" button on the program correctly count and list orders using this reward type.
• Existing reward lines are recalculated so that programs with this reward type do not create extra reward lines and the line discounts stay up to date.

It touches coupon.program, coupon.reward, sale.order and the coupon code wizard sale.coupon.apply.code.