[IMP] point_of_sale: Added customer_note on order lines

In some use cases, the seller in point of sale needs to add a note on an
order line that has to be displayed on the receipt. So we've added a
field on the order line to set a note.

The note is also set on the invoice if the order is invoiced.

closes odoo/odoo#71598

Task-id: 2556994
Signed-off-by: pimodoo <pimodoo@users.noreply.github.com>