refactor: Replace direct error responses with a consistent error response handler in payment processing

[gustaavik]

This pull request refactors error handling and response encoding in the OrderHandler and PaymentHandler classes to improve code consistency and maintainability. The changes replace direct calls to http.Error with reusable helper methods and adjust variable naming for clarity.

Refactoring Error Handling:

• internal/interfaces/api/handler/payment_handler.go: Replaced http.Error calls with h.writeErrorResponse for consistent error handling across multiple methods (CapturePayment, CancelPayment, RefundPayment, ForceApproveMobilePayPayment). Additionally, introduced h.handleValidationError for validating request body errors in ForceApproveMobilePayPayment. [1] [2] [3] [4] [5] [6] [7] [8]

Response Encoding Adjustment:

• internal/interfaces/api/handler/order_handler.go: Renamed the variable orderDTO to response for clarity and consistency in the UpdateOrderStatus method.