Add `run_speech_recognition_seq2seq.py`

[callumm-graphcore]

What does this PR do?

Adds run_speech_recognition_seq2seq.py for training/fine-tuning Seq2Seq speech recognition models, such as Whisper, on the IPU.

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?

[callumm-graphcore]

This should be considered WIP, I need to test it with e.g. whisper-tiny

[callumm-graphcore]

Sorry, should have clarified: this is no longer WIP

[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[katalinic-gc]

The failing test is the one that compares the diff file. Is the current one up to date?

[callumm-graphcore]

The failing test is the one that compares the diff file. Is the current one up to date?

I thought it was, but with the new changes, I'll redo it