Support huggingface_hub v0.x and v1.x
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_7783). All of your documentation changes will be reflected on that endpoint. The docs are available until 30 days after the last update. @lhoestq could you have a look at this PR please? It makes `datasets` compatible with the upcoming `huggingface_hub` v1.0 release while staying compatible with 0.x. Look at PR description for more details.

The CI is currently failing because of 429 rate limit errors but otherwise everything should be fine (made extensive local and ci tests to ensure that). Let me know if you notice anything weird. PR is ready to be merged "as-is" in my opinion.
Related to https://github.com/huggingface/huggingface_hub/issues/3340.

This PR adapts `datasets` to be compatible with both huggingface_hub v0.x and v1.x. 

In practice nothing else should change (I've checked the codebase). The `HfHubHTTPError` is a base error defined in `huggingface_hub` that inherits from `requests.HTTPError` in v0.x and will inherit from `httpx.HTTPError` in v1.x. It has been introduced ~2 years ago so it's fine to use it right now (i.e. no need to wait for v1.x release or bump minimal version).

Most of the changes have been around the test suite to make sure that tests are passing with both `requests` and `httpx` backends. Mid-term it would be good to completely remove the `requests` dependency from `datasets` but that's an orthogonal topic. 