Improve usability in setups that require manual acknowledgement

[jfiedler-jaconi]

I want to use the retry lib functionality in a scenario where I have to perform Rabbit acknowledgement manually. This means that the Rabbit error handler that the lib currently uses is not in play. The only API available to me is to manually feed the error handler simulating the exceptions it would get in the auto-ack scenario. I then have to react to the exceptions thrown by the error handler (for the Rabbit container). See code sample below.

try {
	retryHandler.handleError(new ListenerExecutionFailedException(e.getMessage(), new RetryMessagesException(task.message())));
} catch (ImmediateAcknowledgeAmqpException ex) {
	ack(task);
} catch (AmqpRejectAndDontRequeueException ex) {
	nack(task, false);
}

I suggest to refactor the retry lib a bit such that the publishing of messages for retry becomes more accessible from the outside (if one cannot use the error handler).