Add: decompress csv function in utils.py

[TiffanyCheng27]

No description provided.

[scottbw]

Just a couple of cases worth checking:

1. If called with a path that doesn't end in .gz, it will silently overwrite the original file! So best check it does end in '.gz' and raise an error if it doesn't
2. if the output folder doesn't exist it will raise an error, maybe add a makedirs first?
3. It will silently overwrite the output file it it already exists, maybe again something to check and raise, or at least warn in the logs

[scottbw]

Thanks for putting those guards in, approved.