add Dataset.to_list
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_5611). All of your documentation changes will be reflected on that endpoint. Hi, thanks for working on this! `Table.to_pylist` requires PyArrow 7.0+, and our minimal version requirement is 6.0, so we need to bump the version requirement to avoid CI failure. I'll do this in a separate PR.
close https://github.com/huggingface/datasets/issues/5606

This PR is for adding the `Dataset.to_list` method.
Thank you in advance.
