Force soundfile to return float32 instead of the default float64 
cc @polinaeterna The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_5347). All of your documentation changes will be reflected on that endpoint. Cool ! Feel free to add a comment in the code to explain that and we can merge :) I'm not sure if this is a good change since we plan to get rid of `torchaudio` in the next couple of months... What do you think @polinaeterna @patrickvonplaten ? Models are usually using float32 (e.g. Wev2vec2 in `transformers`) IIRC IMO we can safely assume that float32 is always good enough when using audio models in inference or training. Nevertheless there might be use cases for audio datasets in the future where float64 is needed. 

=> I would by default always cast to float32, but then possible allow the user to cast to float64  > I'm not sure if this is a good change since we plan to get rid of torchaudio in the next couple of months...

@mariosasko I agree but who knows how long we will have to wait until we are really able to do so (https://github.com/bastibe/libsndfile-binaries/pull/17 is a draft. so as @patrickvonplaten is okay with float32, I'd merge.


 @polinaeterna Can you comment on the linked PR to see why it's still a draft? Maybe we can help somehow to get this merged finally.

I think it's weird to align `soundfile` with `torchaudio` when the latter is only used for MP3 (and prob for not much longer). 
(Fixes issue #5345)