Add an attribute to disable custom kernels in deformable detr in order to make the model ONNX exportable
As per title and reported in https://github.com/huggingface/transformers/issues/22330 and https://github.com/huggingface/optimum/pull/931

This option will allow us to patch the model on the fly during the export to avoid going into the try/catch logic that is not supported by PyTorch ONNX export.
_The documentation is not available anymore as the PR was closed or merged._<|||||>@fxmarty Following up on this, I agree with @sgugger's suggestion and think that a config argument would be a better alternative. <|||||>Thank you will update!<|||||>@amyeroberts Let me know if this is better!