Add `IterableDataset.from_generator` to the API
#take Thanks @hamid-vakilzadeh ! Let us know if you have some questions or if we can help Thank you! I certainly will reach out if I need any help.
We've just added `Dataset.from_generator` to the API. It would also be cool to add `IterableDataset.from_generator` to support creating an iterable dataset from a generator.

cc @lhoestq 