INT-3500: Consider to add "error-channel" to the <enricher>

JIRA: https://jira.spring.io/browse/INT-3500

* add 'error-channel' to the <enricher> component
* delegate errorChannel to the internal gateway in ContentEnricher
* added tests for xml based and java based enrichers with error channels

I have signed and agree to the terms of the SpringSource Individual Contributor License Agreement.
This has to be fixed as well. The same timing issue, so `10000` is enough