Fix: Add rate limit to OpenAIAnswerGenerator, change token computation

[Timoeller]

Related Issues

• fixes #3068
• A related PR adjusting the temperatur param as well: https://github.com/deepset-ai/haystack/pull/3073

Proposed Changes:

1. Added a rate limit since otherwise the API will crash eventually.
2. Added a try catch around the API call since OpenAIs API sometimes returns errors
3. Changed prompt length computation, since one has to take the output length into account as well

How did you test it?

manual verification

Checklist

• [x] I have read the contributors guidelines and the code of conduct
• [ ] I have updated the related issue with new insights and changes
• [ ] I added tests that demonstrate the correct behavior of the change
• [x] I've used the conventional commit convention for my PR title
• [x] I documented my code
• [x] I ran pre-commit hooks and fixed any issue

[Timoeller]

Sorry, I realize I won't be able to work on this the next week. I can either look into it afterward or you start taking over?

[Timoeller]

Closing this in favor of https://github.com/deepset-ai/haystack/pull/3398