fix space issue when downloading models

[giacinti]

It may happen that, depending on the model, huggingface-hub creates temporary file chunks before saving the model into the cache. The side effect is that the container /tmp can become full and an error is issued not space left on device. With this change, /tmp is mapped to a local directory with hopefully more space available. I also took the opportunity to update .dockerignore and .gitignore to add the cache directory huggingface and this new temp dir...