feat: direct client payment without configuration

[shadyaziza]

Added new easyPay api

Future<void> easyPay({
    required String checkoutId,
    required BrandType brand,
    required CardInfo card,
  })

Which does not require any configuration from the client side. The possible workflow for this

1. Request checkoutId from the server
2. Client manages the values of CardInfo and BrandType entered by the user through a custom payment form
3. After calling easyPay with the needed data, the client should ask the server about the status of the payment