Expose filename errors in the ETC log

[jonathanthiry]

We return a 400 error when the filename used by a logger doesn't match the pattern we've agreed on with ETC. However, when logger upload data directly, nobody monitors and sees these errors.

This change will append the errors to the log file we provide to ETC.

[ggVGc]

Looks alright, but would prefer keeping the exception handling (logging non-fatal errors) in appendError or appendLogMsgToFile, or at least make those methods return a Try rather than Unit.

[Jonathan-Schenk]

Looks fine and I do not have anything to add. @ggVGc raises a good point I think.

[jonathanthiry]

In 448d1f9, I adjusted the ETC filename parse error logging to write only err.getMessage to errorLog.txt, instead of using UploadResult.extractMessage, because that included stack traces for regular exceptions.