Add optional resume_download argument to help download large models

[Rexhaif]

It's kinda pain to download large models with unstable network connection.
For instance, i've started seeing this type of error (see screenshot). It breaks download process and you have to start again from zero bytes downloaded.

However, cached_download(..) function in huggingface_hub has resume_download argument that can be used to restart download without loosing progress. See this line. So i think it would be helpful to add it as optional argument(defaults to False) to the get_rudalle_model(..) so users can turn it on if they have unstable internet.