Add DETA

[NielsRogge]

What does this PR do?

This PR adds DETA. DETA is a slight change to Deformable DETR by using traditional IoU-based assignment as opposed to the Hungarian matching used in the original DETR, and incorporating NMS (non-maximum suppression) in the postprocessing.

Note: this model has a torchvision dependency for NMS.

To do:

• [ ] transfer checkpoints

[NielsRogge]

cc @alaradirik this PR is in a ready state, except for 2 things:

• [x] whether or not we leverage torchvision's batched_nms => the CI is currently failing because this library is not installed. Will also ask for @sgugger and @LysandreJik's opinion here
• [ ] the post_process_object_detection method might require an in-depth look

[sgugger]

There is no problem with the model requiring torchvision to be installed. We have many models with specific dependencies, some of which you ported yourself ;-). Just protect the import between if is_torchvision_available() and have a the first line in the init of the models be a require_backends(["torchvision"]).

[HuggingFaceDocBuilderDev]

The documentation is not available anymore as the PR was closed or merged.

[NielsRogge]

@sgugger I've addressed all comments, except for adding support for the custom kernel.

Could we perhaps add support for the custom kernel for the 3 models (Mask2Former, OneFormer and DETA) in a separate PR?

[sgugger]

In this case, remove the code trying to load the custom kernels in the modeling file and we can add it back in the PR that will deal with custom kernels.

[NielsRogge]

@sgugger ok, feel free to approve :)

[NielsRogge]

Failing test is unrelated/flaky, merging.