JIRA: https://jira.spring.io/browse/INT-3944
Polishing (PR comments) and Doc Polish
Polishing - PR Comments
Remove custom `async` boolean in favor of the now public setter.
Add exception to `JmsException` hierarchy.
INT-3944: Polishing
* Rename `asyncReplySupported` just to `async`. As well as its getter and setter. Plus fix docs on the matter
* Polishing for the `JmsOutboundGateway` according PR comments
* Rework `JmsOutboundGateway` to return `AbstractIntegrationMessageBuilder` instead of `Message`
since `AbstractMessageProducingHandler` rebuilds `Message` for a new one to copy headers from request
* Add `getPayload()` and `getHeaders()` to the `AbstractIntegrationMessageBuilder` to make the `Routing Slip`
users happy, when the `AbstractIntegrationMessageBuilder` is pushed to the `Routing Slip path` function
* Fix race condition in the `ChatMessageListeningEndpointTests`: the `stanza` parsing is done in the different Thread.
Doc Polishing (Routing Slip)
Fix timing issue in the `LastModifiedFileListFilterTests`:
`Thread.sleep()` not always reflects the reality.
Switch to the "past simulation" via explicit `File.setLastModified()`
4bfcdb9dfa