Support passing arguments to underlying filesystem

[deepyaman]

Description

Motivating Slack conversation:

Q: Is fs_args not supported for the overarching PartitionedDataSet? I need to specify endpoint_url for my S3 interface, and I can do this on other datasets (e.g. pandas.ParquetDataSet) but not on PartitionedDataSet. Without it, I can’t discover partitions.

A: Currently you can put those into credentials as this is the only set of kwargs passed into the filesystem constructor. Would it be acceptable for your use case? I will create a ticket to add fs_args support. Thanks for raising this 👍

Development notes

Checklist

• Read the contributing guidelines
• Opened this PR as a 'Draft Pull Request' if it is work-in-progress
• Updated the documentation to reflect the code changes
• Added a description of this change and added my name to the list of supporting contributions in the RELEASE.md file
• Added tests to cover my changes

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[DmitriiDeriabinQB]

LGTM 👍 But would also be great to add some unit tests, just to make sure that fs_args reach fsspec in the form that we expect. Let me know if any help needed.

[deepyaman]

This branch is somehow orphaned, so I can't continue work here; moving to #559