Revise implementation of RedisMessageListenerContainer.

RedisMessageListenerContainer is now reimplemented using non-blocking synchronization guards and a state management to simplify its maintenances. Additionally, listener registration and subscription setup through the start() method awaits until the listener subscription is confirmed by the Redis server. The synchronization removes potential race conditions that could happen by concurrent access to blocking Redis connectors in which the registration state was guessed and not awaited.

Resolves: #964
Original Pull Request: #2256

Author: mp911de

src/main/asciidoc/reference/redis-messaging.adoc

@@ -47,7 +47,7 @@ Due to its blocking nature, low-level subscription is not attractive, as it requ
 
 `RedisMessageListenerContainer` acts as a message listener container. It is used to receive messages from a Redis channel and drive the `MessageListener` instances that are injected into it. The listener container is responsible for all threading of message reception and dispatches into the listener for processing. A message listener container is the intermediary between an MDP and a messaging provider and takes care of registering to receive messages, resource acquisition and release, exception conversion, and the like. This lets you as an application developer write the (possibly complex) business logic associated with receiving a message (and reacting to it) and delegates boilerplate Redis infrastructure concerns to the framework.
 
- A `MessageListener` can additionally implement `SubscriptionListener` to receive notifications upon subscription/unsubscribe confirmation. Listening to subscription notifications can be useful when synchronizing invocations.
+A `MessageListener` can additionally implement `SubscriptionListener` to receive notifications upon subscription/unsubscribe confirmation. Listening to subscription notifications can be useful when synchronizing invocations.
 
 Furthermore, to minimize the application footprint, `RedisMessageListenerContainer` lets one connection and one thread be shared by multiple listeners even though they do not share a subscription. Thus, no matter how many listeners or channels an application tracks, the runtime cost remains the same throughout its lifetime. Moreover, the container allows runtime configuration changes so that you can add or remove listeners while an application is running without the need for a restart. Additionally, the container uses a lazy subscription approach, using a `RedisConnection` only when needed. If all the listeners are unsubscribed, cleanup is automatically performed, and the thread is released.