HOP-7045 [Bug]: Default values overwrite empty fields in TextFileOutput

[fskorgen]

Moved setting of default values for separator and enclosure from constructor to setDefault
Empty values are now accepted instead of being overridden by defaults

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[hansva]

This will be a broader issue caused by the deserialization changes introduced, while this fix solves the issue for textfileOutput the same issue might be present in other spots. I am looking at a global fix.

[hansva]

should be fixed with #7087