[ONNX] add test images to repo (#63717)

[ONNX] add test images to repo (#63717)

Summary:
This is better than the status quo:
* Test doesn't download files from the internet -> faster and more
  reliable.
* Test doesn't leave the git working directory dirty.

Rather than using the original images, I've copied some images from
the pytorch/vision repo. This will keep the tests in the two repos
in sync, while avoiding adding new assets to the vision repo.

See https://github.com/pytorch/vision/pull/4176.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/63717

Reviewed By: janeyx99

Differential Revision: D30466016

Pulled By: malfet

fbshipit-source-id: 2c56d4c11b5c74db1764576bf1c95ce4ae714574