* INT-3459: Log exceptions in case of failOver
JIRA: https://jira.spring.io/browse/INT-3459
When `UnicastingDispatcher` is configured with `failOver` (true by default),
it loses exceptions it caught with previous handler when the next one
processes message properly
* Add INFO logging for exceptions which are caught before going to fail
over to the next handler
* * Address PR comments
* * More PR comments
* Add a note about this logging into the `channel.adoc`
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