Added onnx config whisper
# What does this PR do?

Fixes # (issue)

This PR adds onnx config and helper functions for export to onnx via optimum and transformers.onnx

_The documentation is not available anymore as the PR was closed or merged._<|||||>@lewtun @echarlaix  The bug is fixed now. The incorrect results were because the export was happening with seqlength 1 due to typo in onnx config generate_dummy_input function.<|||||>Thanks for the review @sgugger and catching those last issues - I've checked the latest changes and think this can now be merged @mht-sharma <|||||>Hello,

I tried to generate onnx model using [docs](https://huggingface.co/docs/transformers/serialization#configuration-based-approach),
To inference, I passed audio features and decoder_input_id , and the output was two array with the shape of (1, 2, 768), (1, 1500, 768). Could you please help me how should I use these outputs for generating transcription? 

Thank you.<|||||>Hi @zara0m please follow the example in this PR for export and  inference using ONNX model. https://github.com/huggingface/optimum/pull/420<|||||>> Hi @zara0m please follow the example in this PR for export and inference using ONNX model. [huggingface/optimum#420](https://github.com/huggingface/optimum/pull/420)

Thank you very much for your help and quick response!

I tested it with base and small model for some non-english audios, but the outputs were not similar to whisper model, or maybe it translates instead of transcribing, how can I fix this?
Also, is there any way that I can have begin/end time of each sentence? (like the transcribe function of whisper model)

Thank you.