RTMDet instance segmentation onnx export support

[mattiasbax]

Hello,

First of all, I'm very impressed by the result of the RTMDet - great work!
I would like to try this out in a C++ environment. But before I put too much time and effort into (seeing as I have little to no experience using MMDetection) I figured I might as well start by asking:

Does the RTMDet Instance Segmentation support onnx export following the proposed methods of exporting the models? (https://github.com/open-mmlab/mmdetection/blob/master/docs/en/tutorials/pytorch2onnx.md)

Thanks!