JIRA: https://jira.spring.io/browse/INT-3620 Add `setShouldAppendNewLine(boolean shouldAppendNewLine)` method to the `FileWritingMessageHandler` class. Added similar test methods to the `FileWritingMessageHandlerTests` class. INT-3620: `appendNewLine` just only for `FileExistsMode.APPEND` Also add `appendNewLine` for `File` payload INT-3620: `appendNewLine` for any `fileExistsMode`