Coupons - Githubissues

As a admin, I can issue coupons so that I can attract users to use our tutoring service.

Acceptance Criteria:

Implement a coupon system to allow users to input coupons into Stripe payment before paying for the service.
Implement a user database check to prevent users from using the same coupon more than once for using the service.
Distribute coupons to registered users who signed up for the newsletter to receive future discounts.