JIRA: https://jira.spring.io/browse/INT-4440
The previous fix eliminated an extra `generateId()` call, but at the
same introduced regression do not populate `id` and `timestamp` from
the serialized state, e.g. after JSON transferring over the network
* Introduce a couple utility methods in the `MutableMessageHeaders`
to extract and parse `id` and `timestamp` from the provided headers
**Cherry-pick to 5.0.x**
(cherry picked from commit ae2aa8b)
2b6cafdba4