Remove unsupported models from Gemini integration

[Amnah199]

Summary and motivation

According to google release notes, the gemini-pro-vision and gemini-ultra model are unsupported. We should update our Gemini integration to support latest models likegemini-1.5-flash.

Tasks

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1. The changes are merged in the main branch (Code + Docstrings)
2. New package version declares the breaking change
3. The package has been released on PyPI
4. Docs at https://docs.haystack.deepset.ai/ were updated
5. Integration tile on https://github.com/deepset-ai/haystack-integrations was updated
6. Notebooks on https://github.com/deepset-ai/haystack-cookbook were updated (if needed)
7. Tutorials on https://github.com/deepset-ai/haystack-tutorials were updated (if needed)
8. Articles on https://github.com/deepset-ai/haystack-home/tree/main/content were updated (if needed)