Method to load Laion400m
### Feature request

Large datasets like Laion400m are provided as embeddings. The provided methods in load_dataset are not straightforward for loading embedding files, i.e. img_emb_XX.npy ; XX = 0 to 99


### Motivation

The trial and experimentation is the key pivot of HF. It would be great if HF can load embeddings files s,ealessly.

### Your contribution

I cam write the loader with some help.