[Request] Load and run onnx model with CV2

[huchenlei]

See Mikubill/sd-webui-controlnet#1892

Because onnxruntime still requires users to install MS Virtual C++, Lvmin suggests that we loads and run onnx model with cv2:
https://docs.opencv.org/4.8.0/d6/d0f/group__dnn.html#ga7faea56041d10c71dbbd6746ca854197

[yzd-v]

We support to run onnx model with opencv in branch opencv_onnx. But we need to manually build OpenCV through cmake to work with GPU. However, according to our test, the speed is also fine with CPU.

[huchenlei]

Thanks! PR landed in ControlNet repo.