feat(core): improve exception handling and validation with Inputs/Outputs

- Added InputOutputValidationException to represent Inputs/Outputs
  validation issues and added handler to it in ErrorsController
- Added support for throwing multiple constraint violations for the same
  input
- Added support for throwing multiple constraints at MultiselectInput
- Refactored exception handling at FlowInputOutput
- Added merge() function to combine constraint violation messages and
  added test for it at InputsTest
- Fixed the failed tests

webserver/src/main/java/io/kestra/webserver/controllers/ErrorController.java

@@ -36,6 +36,10 @@ public class ErrorController {
     public HttpResponse<JsonError> error(HttpRequest<?> request, JsonParseException e) {
         return jsonError(request, e, HttpStatus.UNPROCESSABLE_ENTITY, "Invalid json");
     }
+    @Error(global = true)
+    public HttpResponse<JsonError> error(HttpRequest<?> request, InputOutputValidationException e) {
+        return jsonError(request, e, HttpStatus.UNPROCESSABLE_ENTITY, "Invalid entity");
+    }
 
     @Error(global = true)
     public HttpResponse<JsonError> error(HttpRequest<?> request, ConversionErrorException e) {

webserver/src/main/java/io/kestra/webserver/controllers/api/ExecutionController.java

@@ -2670,7 +2670,12 @@ public class ExecutionController {
         ) {
         }
 
-        public static ApiValidateExecutionInputsResponse of(String id, String namespace, List<Check> checks, List<InputAndValue> inputs) {
+        public static ApiValidateExecutionInputsResponse of(
+            String id,
+            String namespace,
+            List<Check> checks,
+            List<InputAndValue> inputs
+        ) {
             return new ApiValidateExecutionInputsResponse(
                 id,
                 namespace,
@@ -2679,14 +2684,21 @@ public class ExecutionController {
                     it.value(),
                     it.enabled(),
                     it.isDefault(),
-                    Optional.ofNullable(it.exception()).map(exception ->
-                        exception.getConstraintViolations()
-                            .stream()
-                            .map(cv -> new ApiInputError(cv.getMessage()))
+                    // Map the Set<InputOutputValidationException> to ApiInputError
+                    Optional.ofNullable(it.exceptions())
+                        .map(exSet -> exSet.stream()
+                            .map(e -> new ApiInputError(e.getMessage()))
                             .toList()
-                    ).orElse(List.of())
+                        )
+                        .orElse(List.of())
                 )).toList(),
-                checks.stream().map(check -> new ApiCheckFailure(check.getMessage(), check.getStyle(), check.getBehavior())).toList()
+                checks.stream()
+                    .map(check -> new ApiCheckFailure(
+                        check.getMessage(),
+                        check.getStyle(),
+                        check.getBehavior()
+                    ))
+                    .toList()
             );
         }
     }

webserver/src/test/java/io/kestra/webserver/controllers/api/ExecutionControllerRunnerTest.java

@@ -242,7 +242,7 @@ class ExecutionControllerRunnerTest {
         String response = e.getResponse().getBody(String.class).orElseThrow();
 
         assertThat(response).contains("Invalid entity");
-        assertThat(response).contains("Invalid input for `validatedString`");
+        assertThat(response).contains("Invalid value for input `validatedString`");
     }
 
     @Test
@@ -1071,7 +1071,7 @@ class ExecutionControllerRunnerTest {
                 .contentType(MediaType.MULTIPART_FORM_DATA_TYPE)
         ));
         assertThat(exception.getStatus().getCode()).isEqualTo(422);
-        assertThat(exception.getMessage()).isEqualTo("Invalid entity: asked: Invalid input for `asked`, missing required input, but received `null`");
+        assertThat(exception.getMessage()).isEqualTo("Invalid entity: Missing required input:asked");
     }
 
     @Test