Add HuggingFace Datasets to NeMo ASR Dataset script
# Changelog
- Add script to convert HuggingFace ASR datasets to preprocessed NeMo compatible datasets.
- These datasets can then be converted to tarred datasets as always.

# NOTE:
- The converted datasets DO NOT PERFORM TEXT PREPROCESING. That should be handled by the user at manifest level.
- The offline mode dataset transformation is fast but requires 3 copies of the dataset in its entirety at any given time - so it needs a lot of disk space.