ImageConfigAspectRatio:
    | "1:1"
    | "2:3"
    | "3:2"
    | "3:4"
    | "4:3"
    | "4:5"
    | "5:4"
    | "9:16"
    | "16:9"
    | "21:9"
    | "1:8"
    | "8:1"
    | "1:4"
    | "4:1"
    | string & {}

The aspect ratio of the image to generate. Supported aspect ratios: 1:1,

2:3, 3:2, 3:4, 4:3, 9:16, 16:9, 21:9.

If not specified, the model will choose a default aspect ratio based on any reference images provided.