Add iter_archive
Added the `iter_archive` method for the StreamingDownloadManager.

It was already implemented in the regular DownloadManager.
Now it can be used to stream from TAR archives as mentioned in https://github.com/huggingface/datasets/issues/2829

I also updated the `food101` dataset as an example.
Any image/audio dataset using TAR archives can be updated to use `iter_archive` in order to be streamable :)

cc @severo 

Fix #2829.