Add optional s3fs / gcfs as optional dependencies

[praateekmahajan]

Is your feature request related to a problem? Please describe.
If customers want to use NeMo Curator on Cloud we should add optional groups as s3 or gc that installs the correct version inline with our existing fsspec installation. If users install themselves using pip, it might be possible that Curator needs fsspec=2024.12 while pip as an additional install of s3fs installs 2025.12

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