DSL-(S)FTP-Namespace-Builder-Factory

**DO NOT MERGE YET**.

There is need to provide tests on the matter.

(S)FTP Tests

* Add test cases for (s)ftp components based on embedded (S)FtpServers
* Upgrade some dependencies
* Fix bug in the `IntegrationFlowBeanPostProcessor` for the registration internal (a result of `MessageSourceSpec`) as a bean in the AC