Add support for WebP images

[HendricksJudy]

Fixes #135

Add support for WebP images.

• demo/configs/webpack/common.js

  • Add webp to the test array in the rule for image files.
  • Update the image-webpack-loader configuration to support WebP images.

• demo/src/App.tsx

  • Update the loadImage function to handle WebP images.
  • Add error handling for WebP images.

• scripts/amg.py

  • Update the cv2.imread function to support WebP images.
  • Add conditional handling for WebP images in cv2.cvtColor.

• scripts/export_onnx_model.py

  • Import cv2 module.
  • Update the cv2.imread function to support WebP images.
  • Add conditional handling for WebP images in cv2.cvtColor.