improvements for nano banana

[narengogi]

Description: (required)

• allow users to pass image_config parameter when making requests to nano banana models

Tests Run/Test cases added: (required)

• payload

{
    "model": "gemini-2.5-flash-image",
    "max_tokens": 32768,
    "stream": false,
    "modalities": [
        "text",
        "image"
    ],
    "image_config": {
        "aspect_ratio": "16:9",
        "image_size": "2K"
    },
    "messages": [
        {
            "role": "system",
            "content": "Say Hi"
        },
        {
            "role": "user",
            "content": [
                {
                    "type": "text",
                    "text": "Add some sugar powder to the croissants. Include text across the top of the image that says \"Made Fresh Daily\"."
                },
                {
                    "type": "image_url",
                    "image_url": {
                        "url": "gs://cloud-samples-data/generative-ai/image/croissant.jpeg"
                    }
                }
            ]
        }
    ]
}

Type of Change:

• New feature (non-breaking change which adds functionality)