Updated the PaymentType property in PublicWalkRequestAcceptDto and WalkCreateDto to be nullable.
Modified ApiWalksController to safely assign PaymentType, using a default value when null to prevent runtime errors.
Significant updates to WalkService.cs for improved fee handling and voucher processing. Introduced API version 3 in ApiAccountController.cs with new user registration and external login endpoints, supporting Google and Apple. Added functionality for setting user types without creating MangoPay users.
- Updated `Walk` class to include `PaymentType` property.
- Introduced `WalkPaymentTypeDto` enum for payment types.
- Modified DTOs (`PublicWalkRequestAcceptDto`, `WalkCreateDto`, `WalkDto`, `WalkWithNamesDto`) to include `PaymentType`.
- Enhanced `ApiWalksController` with new endpoints for accepting and canceling walks, and confirming walks with ratings.
- Updated `MappingProfile` for seamless conversion between `WalkPaymentType` and `WalkPaymentTypeDto`.
