Support remote data files
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@lhoestq maybe we could also use (if available) the ETag of the remote file in `create_config_id`? > @lhoestq maybe we could also use (if available) the ETag of the remote file in `create_config_id`?

Sure ! We can get the ETag with
```python
headers = get_authentication_headers_for_url(url, use_auth_token=use_auth_token)  # auth for private repos
etag = http_head(url, headers=headers).headers.get("ETag")
```

Since the computation of the `config_id` is done in the `DatasetBuilder.__init__`, then this means that we need to add a new parameter `use_auth_token` in `DatasetBuilder.__init__`

Does that sound good ? We can add this in a following PR
Add support for (streaming) remote data files:

```python
data_files = f"https://huggingface.co/datasets/{repo_id}/resolve/main/{relative_file_path}"
ds = load_dataset("json", split="train", data_files=data_files, streaming=True)
```

cc: @thomwolf 
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