Add test-datasets CI job
_The documentation is not available anymore as the PR was closed or merged._ Closing this one since the dataset scripts will be removed in https://github.com/huggingface/datasets/pull/4974
To avoid having too many conflicts in the datasets and metrics dependencies I split the CI into test and test-catalog

test does the test of the core of the `datasets` lib, while test-catalog tests the datasets scripts and metrics scripts

This also makes `pip install -e .[dev]` much smaller for developers

WDYT @albertvillanova ?