Add example of using images in sample

[pamelafox]

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I found this example in promptflow repo: https://github.com/microsoft/promptflow/blob/7f918110ebd61241001bd2d00ad9ec1dbb516726/src/promptflow/tests/test_configs/prompty/prompty_with_image.prompty#L20

Perhaps you can move that here, or make a similar one?