Load sharded pt to flax
# What does this PR do?
Add conversion to `flax` from sharded `pytroch` checkpoints. Follows #18026  which was closed to rename the branch (no really necessary, sorry for the inconvenience). Should fix #17537

_The documentation is not available anymore as the PR was closed or merged._<|||||>Okay 👍🏻  Thanks for the review gonna fix that asap ! 