Fix breaking change in `onnxruntime` for ONNX quantization
Using `onnxruntime.quantization.quantize` has been deprecated since a while:

```
WARNING:root:onnxruntime.quantization.quantize is deprecated.
         Please use quantize_static for static quantization, quantize_dynamic for dynamic quantization.
```

and has been removed from `onnxruntime` in v1.12.0 (released 6 days ago). This breaks quantization in `transformers.convert_graph_to_onnx`.

I have migrated `onnxruntime.quantization.quantize` to `transformers.convert_graph_to_onnx.quantize` to preserve compatibility.


## Who can review?
@mfuntowicz 
_The documentation is not available anymore as the PR was closed or merged._<|||||>@JingyaHuang @lewtun @michaelbenayoun Happy to implement changes if you have any suggestions 😊 <|||||>Thanks @lewtun :pray: All tests are passing on my machine:

![image](https://user-images.githubusercontent.com/16133277/185413954-4a41a3ee-c6b3-41bd-a887-107ef1a66be0.png)
