Unified REST API: Replace sortOrder Field with Enum in SearchQuerySortRequest

[houssain-barouni]

Description

We need to update the sortOrder field in the SearchQuerySortRequest from a string type to an enum with possible values asc and desc in our OpenAPI specification. The default value should be asc. Additionally, we need to ensure that the API validation correctly returns a 400 Bad Request with an appropriate ProblemDetail object when an invalid value is provided.

Acceptance Criteria

• The sortOrder field in the SearchQuerySortRequest is an enum with values asc and desc, and the default is asc.
• The API returns a 400 Bad Request with a ProblemDetail object when an invalid sort order value is provided.
• Unit tests (ProcessInstanceControllerTest) are passing/updated with the new validation logic.

Implementation proposal

We can use an ExceptionHandler on MethodArgumentNotValidException to identify the invalid input field

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(MethodArgumentNotValidException.class)
    public ResponseEntity<ProblemDetail> handleValidationExceptions(MethodArgumentNotValidException ex) {
        for (FieldError error : ex.getBindingResult().getFieldErrors()) {
            if ("sortOrder".equals(error.getField())) {
                // return the problem Detail with the invalid sortOrder
            }
           ...
        }

[tmetzke]

Unassigning @houssain-barouni for now, anyone can tackle this