Add multi-image upload

[alexrudall]

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[fearlessfrog]

This works nicely for me with image array inputs e.g.

      client = OpenAI::Client.new
      response = client.images.edit(
        parameters: {
          model: "gpt-image-1",
          image: [File.open(base_image_path, "rb"), File.open(logo_image_path, "rb")],
          prompt: "Take the first image as base and apply the second image as a watermark on the bottom right corner",
          size: "1024x1024"
          # Removed response_format parameter as it's not supported with gpt-image-1
        }
      )

Thanks!