[IMP] point_of_sale: add extendable method
[IMP] point_of_sale: add extendable method

To build the key when grouping data for account move line creation

Closes #17596

ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo,ygol/odoo