Looking forward exporting Mask2Former to ONNX

Describe the feature

Motivation

1. Many detection & sematic segmentation classical methods（e.g yolo,centernet, deeplabv3,ocrnet）has already support exporting to onnx and made a huge contribution for academia and industry field. But for panoptic segmentaion, mmlab series are still not ready for that yet
2. sota mask2former is a great achievement for panoptic segmentaion( e.g transformer) . It will be wonderful if can be export to onnx（swin transfomer backbone） for depolyment

Related resources

If there is an official code release or third-party implementations, please also provide the information here, which would be very helpful. https://github.com/facebookresearch/Mask2Former https://github.com/open-mmlab/mmdetection/tree/master/configs/mask2former