Fixes: https://github.com/spring-projects/spring-integration/issues/5123
When `RedisMessageStore`, for example, adds and removes messages, it operates on two keys separately, which may cause problems in multi-threading due to non-atomic operations.
Although using Redis to delay messages is not a good idea, the abnormal loss of messages in the logs alerted me when the number of requests was not large.
By comparing the logs, the problem that the message group representing the metadata is not consistent with the actual message.
A simple solution is to add lock like in the `SimpleMessageStore`, which is also the approach taken in this pull request.
* Add `LockRegistry` to `AbstractMessageGroupStore`
* Normalize access levels and method name about the lock of `MessageGroupStore`
* Add document about the lock of `AbstractMessageGroupStore`
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