feat: changing default model from gpt-3.5-turbo` to `gpt-4o-mini`

[davidsbatista]

Related Issues

• part of https://github.com/deepset-ai/haystack/issues/8222

How did you test it?

• local unit tests and CI tests

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[coveralls]

Pull Request Test Coverage Report for Build 10833065031

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 93.973%

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Totals
Change from base Build 10792993710:	0.0%
Covered Lines:	3352
Relevant Lines:	3567

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💛 - Coveralls