Add WebGPU version of gpt-oss-20b ONNX to model list

[dsjlee]

Can we get WebGPU version of ONNX model for gpt-oss-20b added to official model list?
Model weight seems to have already been published in huggingface as of Jan 16th:
https://huggingface.co/onnxruntime/gpt-oss-20b-onnx/tree/main/webgpu