[IMP] website_sale: confirm quotation only when the payment is done, not directly when hitting 'pay now'.

- Task: https://www.odoo.com/web#id=9613&view_type=form&model=project.task&action=333&active_id=248
- Pad: https://pad.odoo.com/p/r.RToSTsy5RBcb6yR1