[IMP] various: improve section and add note on sale order and invoice

Enterprise counterpart of this commit: https://github.com/odoo/odoo/commit/762adedece1c6c2b97b282348659c1b39b988d24

In enterprise the commit will also remove most of the features of website_quote_subscription because they became obsolete with the ability to create sections.

Indeed the feature was to automatically regroup recurring subscriptions in a "section" at the bottom of the documents. Now if the sale persons want that behavior they can just create an actual section.

Task #53996
PR #2276

models/sale_coupon_program.py

@@ -214,7 +214,7 @@ class SaleCouponProgram(models.Model):
         i.e Buy 1 imac + get 1 ipad mini free then check 1 imac is on cart or not
         or  Buy 1 coke + get 1 coke free then check 2 cokes are on cart or not
         """
-        order_lines = order.order_line - order._get_reward_lines()
+        order_lines = order.order_line.filtered(lambda line: line.product_id) - order._get_reward_lines()
         products_qties = dict.fromkeys([product for product in order_lines.mapped('product_id')], 0)
         for line in order_lines:
             products_qties[line.product_id] += line.product_uom_qty