Image support in `GoogleGenAIChatGenerator`

[anakin87]

We want to make this component support multimodal user messages.

Relevant info: https://ai.google.dev/gemini-api/docs/vision?lang=python

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Reference implementations

• OpenAI
• Bedrock

[vblagoje]

Fix is in https://pypi.org/project/google-genai-haystack/2.1.0/