WebFluxRequestExecutingMessageHandler directly creates WebClientResponseException rather than using provided create(...) factory method

[djgraff209]

In what version(s) of Spring Integration are you seeing this issue?

5.3.8.RELEASE

Describe the bug

The WebFluxRequestExecutingMessageHandler is directly creating a WebClientResponseException rather than using the provided create factory methods. This can cause some confusion when attempting to use the customizeMonoReply method to trap and provide a default response payload.

To Reproduce

Assume a RESTful endpoint that will return an HTTP/404 error when an entity is not found.

Using an integration flow similar to the following:

@Bean
public IntegrationFlow getMixEntryFlowReactive() {
    final WebClient webClient =
                        webClientBuilder.defaultHeaders(
                                        headers -> headers.setBasicAuth("api", "s3cr3t")
                                    )
                                    .build();
    final String defaultPayload = "{ \"id\": -1, \"name\": null }";
    return f->
            f.enrich(
                e -> e.requestSubFlow(
                    sf -> sf.handle(
                        WebFlux.outboundGateway("http://localhost:8080/mix-entry/name/{mixEntryName}", webClient)
                        .httpMethod(HttpMethod.GET)
                        .uriVariable("mixEntryName", "payload")
                        .expectedResponseType(String.class)
                        ,
                        ec -> ec.customizeMonoReply(
                            (Message<?> message, Mono<?> mono) -> 
                                mono.onErrorResume(
                                    WebClientResponseException.NotFound.class,
                                    ex1 -> Mono.just(ex1)
                                                .map(ex -> defaultPayload)
                                                .switchIfEmpty((Mono)mono)
                                )
                        )
                    )
                    .logAndReply()
                )
                .headerExpression("mix-entry-id", "#jsonPath(payload, '$.id')")
        )
        .logAndReply();
}

Expected behavior

Expectation is that resulting message, when an HTTP/404 error occurs, contains the header mix-entry-id with the value of -1.

Sample

https://github.com/djgraff209/so68637283