Finish deprecating the fs argument
See #5385 for some discussion on this

The `fs=` arg was depcrecated from `Dataset.save_to_disk` and `Dataset.load_from_disk` in `2.8.0` (to be removed in `3.0.0`).  There are a few other places where the `fs=` arg was still used (functions/methods in `datasets.info` and `datasets.load`).  This PR adds a similar behavior, warnings and the `storage_options=` arg to these functions and methods.

One question: should the "deprecated" / "added" versions be `2.8.1` for the docs/warnings on these?  Right now I'm going with "fs was deprecated in 2.8.0" but "storage_options= was added in 2.8.1" where appropriate.

@mariosasko 