MessageChannelBinder support for futures

Following is related to: https://github.com/SolaceProducts/solace-spring-cloud/issues/35

I want to do some brain storming how to solve this problematic most elegant.

The Problem:

• When sending a message to broker
• The response from broker if the messages was accepted gets async
• This leads currently to that not submitted messages will only be reported on error channel
• But this makes it very hard for the application to handle those problem, caused by the missing relation.

Possible improvement A:

https://github.com/spring-projects/spring-integration/blob/a66e82b0aad0eb3ffb909dd5568c14b6713259c0/spring-integration-core/src/main/java/org/springframework/integration/channel/AbstractSubscribableChannel.java#L70

@Override
protected boolean doSend(Message<?> message, long timeout) {
    try {
        CompletableFuture<MessaggingExecption> asyncErrorConsumer = new CompletableFuture<>();
        message.getHeaders().add(MessageHeaders.ERROR_CONSUMER, asyncErrorConsumer);
        
        boolean result = getRequiredDispatcher().dispatch(message);
        
        if (!result) {
          return result;
        }  
        
        MessagingException possibleError = asyncErrorConsumer.get(timeout, TimeUnit.SECONDS);
        if (possibleError != null) {
          throw possibleError;
        }
    
        return result;
    }
    catch (MessageDispatchingException ex) {
        String description = ex.getMessage() + " for channel '" + getFullChannelName() + "'.";
        throw new MessageDeliveryException(message, description, ex);
    }
}

• The code is everything not nice
• It is a breaking change that all binders have to implement
• The benefit of async message persistant confirmation is gone for all producer wanting fire and forget

Possible improvement B:

Rewrite all the sender code including StreamBridge to not return "boolean" but instead "Future"

• Big refactoring in spring-cloud-stream and spring-integration-core
• Breaking change for all binder
• Allows applications to make fire and forget as well as wait for confirmation that the message was persisted/accepted

Possible improvement C:

An äquivalent to:
https://docs.spring.io/spring-cloud-stream-binder-rabbit/docs/3.1.0/reference/html/spring-cloud-stream-binder-rabbit.html#publisher-confirms

But i opened this issue to find a better solution that also could be used from rabbit.

• A developer can choose if he wants a confirmation.
• Its not very straight forward. (Not easy to understand)
• No changes on spring framework.

Start by reading the referenced AbstractSubscribableChannel.java implementation and the sender code in spring-cloud-stream, including StreamBridge. Compare the proposed CompletableFuture and Future approaches with the Rabbit publisher-confirms behavior. Done requires an agreed API and implementation scope, plus identified tests for asynchronous confirmation and fire-and-forget behavior.