GitLab

* First draft

* More improvements

* Add conversion script

* More improvements

* Add docs

* Address review

* Rename class to ConvEncoder

* Address review

* Apply suggestion

* Apply suggestions from code review
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* Update all DETR friends

* Add corresponding test

* Improve test

* Fix bug

* Add more tests

* Set out_features to last stage by default
Co-authored-by: Niels Rogge <nielsrogge@Nielss-MacBook-Pro.local>
Co-authored-by: Niels Rogge <nielsrogge@Nielss-MBP.localdomain>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>