[Research] Speed up evaluation for XTREME-S
# What does this PR do?

This adds a couple of improvements to the evaluation parts of the XTREME-S script:
* fix the bug where filtering by language happened multiple times for parallel workers (redundantly)
* use `preprocess_logits_for_metrics` to transform the logits into pred_ids before concatenating them to avoid OOMs
* add the `--language_group` parameter to train on the FLEURS dataset in batches of languages (west/eastern european languages, south asian languages etc.)

Misc:
* add `--ctc_zero_infinity` to handle the noisy FLEURS transcriptions
_The documentation is not available anymore as the PR was closed or merged._<|||||>@patrickvonplaten these are ready to merge now I think 

Also cc @sanchit-gandhi: the fixes should make your life much easier if you decide to do a run of multilingual translation :)