Reactive programming support

[carlopolisini]

Hi, I am using your library in a project. We have some Reactive code that returns Mono/Flux publishers, the point is that if in execute block I call that Java method and then subscribe() in a not-blocking way, then in case of an error there is no way to re-schedule a task since the Mono/Flux executes in another thread and the exception can't bubble up to the ExecutePicked class that call the failure() method.
The only workaround I have found now is to call the .block() on the Mono/Flux. Do you eventually plan to have better core support for Reactive?

Tasks.recurring(MONTHLY_TASK)
.onFailure(new FailureHandler.MaxRetriesFailureHandler<>(
                        MONTHLY_TASK_MAX_RETRIES,
                        new FailureHandler.ExponentialBackoffFailureHandler<>(
                                Duration.ofMinutes(MONTHLY_TASK_BACKOFF_FAILURE_MINUTES))))
.execute((instance, ctx) -> {
                    myAppService.generateReport()
                        .onErrorMap(throwable -> {
                            LOG.error("Error report generation", throwable);
                            return throwable; // It isn't catched by ExecutePicked, how to reschedule in asynch way?
                        })
                       .subscribe(); 
                });

Actual workaround:

`Tasks.recurring(MONTHLY_TASK)
.onFailure(new FailureHandler.MaxRetriesFailureHandler<>(
                        MONTHLY_TASK_MAX_RETRIES,
                        new FailureHandler.ExponentialBackoffFailureHandler<>(
                                Duration.ofMinutes(MONTHLY_TASK_BACKOFF_FAILURE_MINUTES))))
.execute((instance, ctx) -> {
                    myAppService.generateReport().block(); 
                });

Reactive function

public Mono<Void> generateReport() {...}