100% discount can now be offered using coupon codes

Added the ability to create a 100% off coupon code
The end customer can redeem a coupon code to get a 100% off on the cart value. They would still require to enter their card details to save credit card info in case it is required for upsells in the next steps
Only Stripe can be used to give 100% off on order amounts, this will not work with Paypal. In case both Stripe and Paypal exist, the Paypal option will be hidden.
A small text
Card details will be used for verification purposes
will appear beside the card element during a $0 checkout