Enforce compression extensions for CSV Files

[pdet]

When writing a compressed CSV file, the correct extensions will be enforced.

For gzip: .csv.gz
For zstd: .csv.zst

One potential downside is that users won't be able to write a gzipped file that ends with something different than .csv.gz, or .csv.zst for zstd. Is this flexibility important?

The other issue is that I could imagine JSON and other file formats having the same issue, so maybe this implementation check should happen at a higher level.

[Mytherin]

Thanks for the PR!

I think as you mentioned this is indeed not the right location for this fix. The problem is specifically for PARTITION_BY since the user only specifies a directory there instead of a file to write to. The extension is set in the BindCopyTo. The correct solution here seems to me to change which extension is selected if compression is selected.