Consider adding utf-8 support to `prtvol2csv`

[mferrera]

We could consider adding support for iso-8859-1 encoded files more broadly, attempting to parse at utf-8 and on a decoding error fall back to iso-8859-1.

[mferrera]

The original error is a result from res2df, but can still be relevant here.

[berland]

This was debated a lot during the transition from Python2 to Python3, and was downvoted. It occurred much more frequently before, now these issues are rare.