Register `.zstd` extension for zstd-compressed files
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_7032). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. @albertvillanova hm I don't know tbh, it's just that "mlfoundations/dclm-baseline-1.0" dataset contains [files](https://huggingface.co/datasets/mlfoundations/dclm-baseline-1.0/tree/main/global-shard_01_of_10/local-shard_0_of_10) with this extension and these files seem to be valid  not sure why CI is failing but seems to be unrelated to this pr? can I merge @lhoestq @albertvillanova ? yes you can merge, the CI failure is unrelated (surely an issue with hub-ci) ah why not, you could try opening a PR

btw there is a channel with them at (internal) https://app.slack.com/client/T1RCG4490/C079AKTV11P if you want to let them know @lhoestq, your previous comment was addressed to me or Polina?

@polinaeterna let me know if it is OK for you. I opened https://huggingface.co/datasets/mlfoundations/dclm-baseline-1.0/discussions/7 Should we close this PR then?
For example, https://huggingface.co/datasets/mlfoundations/dclm-baseline-1.0 dataset files have `.zstd` extension which is currently ignored (only `.zst` is registered).