Fixes FrugalScore
The docs for this PR live [here](https://moon-ci-docs.huggingface.co/docs/datasets/pr_4305). All of your documentation changes will be reflected on that endpoint. > predictions and references are swapped. Basically Frugalscore is commutative, however some tiny differences can occur if we swap the references and the predictions. I decided to swap them just to obtain the exact results as reported in the paper.

What is the order of magnitude of the difference ? Do you know what causes this ?

> I switched to dynamic padding that was was used in the training, forcing the padding to max_length introduces errors for some reason that I ignore.

What error ?
There are two minor modifications in this PR:
1) `predictions` and `references` are swapped. Basically Frugalscore is commutative, however some tiny differences can occur if we swap the references and the predictions. I decided to swap them just to obtain the exact results as reported in the paper.
2) I switched to dynamic padding that was was used in the training, forcing the padding to `max_length`  introduces errors for some reason that I ignore.

@lhoestq 