Add an API to register objects to Auto classes (#13989)
* Add API to register a new object in auto classes
* Fix test
* Documentation
* Add to tokenizers and test
* Add cleanup after tests
* Be more careful
* Move import
* Move import
* Cleanup in TF test too
* Add consistency check
* Add documentation
* Style
* Update docs/source/model_doc/auto.rst
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
* Update src/transformers/models/auto/auto_factory.py
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
Co-authored-by: Lysandre Debut <lysandre@huggingface.co>
