Fix bug when adding Whisper to wheel (#15708)
### Description
This PR adds `onnxruntime.transformers.models.whisper` to the wheel.
### Usage
There is a README.md document that shows sample commands. The following
command will show how to use the custom Whisper export script in more
detail.
```
$ python3 -m onnxruntime.transformers.models.whisper.convert_to_onnx --help
```
### Motivation and Context
This fixes an issue with adding the Whisper custom export scripts to the
wheel. The Whisper folder now appears in the wheel.
