New page for payment methods in the client app

A separate page has been added where customers can view their linked payment methods. This gives customers better insight into the payment details associated with their account and lays the foundation for more extensive management of payment methods in the client app.

In a future expansion, customers will also be able to manage their own bank accounts, link new payment methods, and adjust payment methods for subscriptions. This makes it easier for customers to keep their payment details up to date, and reduces the manual work involved for coaches and studios regarding payment changes.