[Feature][WIP] add onnxslim support

[inisis]

What does this PR do?

Hi, we have developed a tool called onnxslim, which can help slim exported onnx model. I want to slim onnx model so we can achieve better performance, I have tested provided cases, and after onnxslim, we can achieve about 3% performance gain, and also I have tested models under exporters/onnx/test_onnx_export.py, after onnxslim, there will be an average 10% op number decrease.

And this pr fix a bug when exporting sd models.

Fixes #1744

Before submitting

• This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
• Did you make sure to update the documentation with your changes?
• Did you write any new necessary tests?

Who can review?

@fxmarty, @echarlaix, @JingyaHuang, @michaelbenayoun

@xenova @glenn-jocher, the author of transformer.js and ultralytics where onnxslim is already merged.