GitLab

* New run_seq2seq script

* Add tests

* Mark as slow

* Update examples/seq2seq/run_seq2seq.py
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* Update src/transformers/data/data_collator.py
Co-authored-by: Suraj Patil <surajp815@gmail.com>

* Update src/transformers/data/data_collator.py
Co-authored-by: Suraj Patil <surajp815@gmail.com>

* Address review comments
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>
Co-authored-by: Suraj Patil <surajp815@gmail.com>