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.
- 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`.
