[Discounts] Display the discount field on the Cart page

The hypothesis is that the user who has obtained a discount code will not know how or where to apply the discount code. All users going through the Cart page and seeing that they cannot apply the discount code they have received will hesitate to proceed to checkout (not knowing that they can apply the discount code at checkout).

The hypothesis is that by applying the discount code directly on the Cart page the user will feel more motivated to proceed to checkout, feeling the amount they save immediately, often associating the amount displayed on the Cart page as the amount to be paid, which is false, if the discount code can be applied at checkout.