Allow select in GPT ImageGen the output size and quality

The OpenAi Image generation support:

• edition

• Size: Image dimensions (e.g., 1024x1024, 1024x1536)

• Quality: Rendering quality (e.g. low, medium, high)

• Format: File output format

• Compression: Compression level (0-100%) for JPEG and WebP formats

• Background: Transparent or opaque