JIRA: https://jira.spring.io/browse/INT-4113
* To simplify `MessagePublishingErrorHandler` and avoid extra `PollerMetadata` beans, added the `errorChannel()` attribute to the `@Poller` annotation
* The `MessagePublishingErrorHandler` now supports the late-binding via new `defaultErrorChannelName`
* Docs about new `errorChannel()` attribute
* Some other docs polishing
Polishing
**Cherry-pick to 4.3.x**
Polishing docs according PR comments