[LW-DETR] Fix training (#44441)
* Fix training
* Investigate more
* Fix LW-DETR two-stage bbox gradient flow
* Add training scripts
* Remove unwanted files
* pad class scores as well
* Update pyproject
* Add progress
* Remove scripts
* Restore pyproject
* Restore config docstring
* Restore config docstring
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Co-authored-by: yonigozlan <yoni.gozlan@huggingface.co>
