Implement payment features (Paypal, Stripe)

[steph-koopmanschap]

Implement paypal or stripe payment features into the app.

Related:
https://github.com/steph-koopmanschap/jasma/blob/development/backend/api/views/payment_views.py

the bought credits should be stored in the
balance = models.DecimalField(max_digits=19, decimal_places=4, default=0, validators=[MinValueValidator(0)]) field in the User model in models.py

Transaction info should be stored in the Transaction model in models.py

https://github.com/steph-koopmanschap/jasma/blob/development/backend/api/models.py

Stripe Payment documentation
https://stripe.com/docs/payments/checkout/how-checkout-works

https://stripe.com/docs/payments/checkout/fulfill-orders

Paypal API documentation
https://developer.paypal.com/api/rest/

Postman API collection for Paypal
https://postman.com/paypal/collection/19024122-92a85d0e-51e7-47da-9f83-c45dcb1cdf24