JIRA: https://jira.spring.io/browse/INT-4117
Add an option to set file permissions on the `FileWritingMessageHandler` when the file system supports it.
Polishing - PR Comments; more robust file system detection.
Add DSL support and fix NPE with missing timestamp header.
Fix javadoc
Fix javadoc
Some polishing:
* Add `chmod >= 0` assertion
* Make some assertion with string concatenation as `Supplier`-based to
deffer that string concatenation
2b99c191f6