Writing layer for NonMaxSuppression in onnx parser

I found a working solution.
The documentation fails to mention that BatchedNMSPlugin is modeled directly after TensorFlow CombinedNonMaxSuppression:

as compared to

So I modified my TF model to use CombinedNMS, then wrote a script using ONNX Graphsurgeon that convert nodes from CombinedNonMaxSuppression to BatchedNMSDynamic_TRT based on the the following mapping from the tf2tensorrt code: