Fix circular import in onnx.utils
# What does this PR do?

This PR fixes the circular import in `onnx.utils` that one can experiment right now with:
```py
from transformers.onnx import OnnxConfig
```

It comes form the fact that `onnx.utils` imports `AutoProcessor`, `AutoFeatureExtractor` and `AutoTokenizer`, which then requires all models to be initialized, which in turns requires all configs to be initialized and relies on `OnnxConfig`, hence a circular import.

Supercedes #17576 
_The documentation is not available anymore as the PR was closed or merged._