Generate coupons in another coupon program in sales

This module extends the coupon and promotion features of Odoo Sales. When a promotion is configured so that its reward coupon should actually be issued by another promotion (the "next" program), the module changes what happens at checkout.

• The reward coupon is created in the destination promotion rather than in the promotion that triggered it, so the rules used to apply the coupon can differ from the rules used to generate it.
• The sales counter shown on the destination promotion reflects the sales of the promotion that points to it, so the numbers stay meaningful.
• The button that opens the related sales orders from a promotion opens the orders of the destination promotion instead.
• Coupons that were generated but whose promotion is no longer applied on the order are automatically set to expired and removed from the order's generated coupons, avoiding leftover valid coupons.

It touches the coupon.program and sale.order models. No new menus or screens are added; the behaviour appears inside the existing promotion configuration and sales order flows.