Add discount percentage

We are missing the option to have discounts calculated automatically by Salesbuildr (SB). Currently, we have to calculate the discount percentage manually, which is cumbersome.

It would be ideal if we could enter a percentage into the discount field, after which SB automatically applies the calculation to the total amount. This field is currently greyed out and uneditable, forcing us to calculate the discount ourselves. It would save a lot of time if SB could automate this process.