Issue: Only user permission of saved cache files, not group

Comment:
Hello, I'm working on a project with a very similar setup to the one mentioned by @siddk, namely we have a shared cache directory in the team that we wish to use to avoid redundant dataset downloads. However, we're hitting `PermissionError` when one member of the team tries to reload a dataset that was downloaded by another team member (stack trace below).

Concretely, we first create a shared directory and give everyone read, write, execute permissions as follows (I know this isn't best practice 🤫):

```shell
mkdir shared-folder
chmod -R 777 shared-folder
```

We then set the following in our `.bashrc` profiles:

```
# Hugging Face caches
export HUGGINGFACE_HUB_CACHE=/path/to/shared-folder
export HF_DATASETS_CACHE=/path/to/shared-folder

# For shared access to the shared-folder directory
umask 000
```

Now, running e.g. `load_dataset("emotion")` the first time works (as expected), but when another team member tries to load from cache we get something like:

```
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 1759, in load_dataset
    builder_instance = load_dataset_builder(
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 1496, in load_dataset_builder
    dataset_module = dataset_module_factory(
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 1218, in dataset_module_factory
    raise e1 from None
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 1193, in dataset_module_factory
    ).get_module()
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 903, in get_module
    local_path = self.download_loading_script()
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/load.py", line 871, in download_loading_script
    return cached_path(file_path, download_config=download_config)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/utils/file_utils.py", line 210, in cached_path
    output_path = ExtractManager(cache_dir=download_config.cache_dir).extract(
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/utils/extract.py", line 42, in extract
    extractor_format = self.extractor.infer_extractor_format(input_path)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/utils/extract.py", line 287, in infer_extractor_format
    if extractor.is_extractable(path, magic_number=magic_number):
  File "~/miniconda3/envs/llama-nol/lib/python3.10/site-packages/datasets/utils/extract.py", line 84, in is_extractable
    return tarfile.is_tarfile(path)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/tarfile.py", line 2517, in is_tarfile
    t = open(name)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/tarfile.py", line 1632, in open
    return func(name, "r", fileobj, **kwargs)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/tarfile.py", line 1698, in gzopen
    fileobj = GzipFile(name, mode + "b", compresslevel, fileobj)
  File "~/miniconda3/envs/llama-nol/lib/python3.10/gzip.py", line 174, in __init__
    fileobj = self.myfileobj = builtins.open(filename, mode or 'rb')
PermissionError: [Errno 13] Permission denied: '/path/to/shared-folder/downloads/4e7db366b1ea045d0faa083a2e47ac87326ad8e653f894763b0982c2a1e94078.cc96367835404d4195bf75b2602e6dbbfd2da9288170fc0b2298fc0e376ff52a.py'
```

If I understand this comment from @bhavitvyamalik:

> Yeah sure! Instead of using default `0o644` should I first extract umask of current user and then use `os.umask` on it? We can do it inside `Dataset` class so that all folders/files created during the call use running user's umask

the goal was to infer the `umask` of the user profile, but perhaps I misunderstood and the true solution is to chmod the `cache_files` as @lhoestq suggests above - is that correct?

cc @natolambert @nazneenrajani @edbeeching