自动排列组合生成带透明通道的图层图片，批量生成。
- output_dir: 输出目录
- assets_dir: 图片素材根目录
- layer_index: 图层层级，1表示最低层
- directory: 图层图片所在目录
- image_mode: 图片模式
{
"output_dir": ".\\NFT_Faces",
"assets_dir": ".\\assets",
"parts": [
{
"layer_index": 1,
"directory": "clothes"
},
{
"layer_index": 2,
"directory": "face"
},
{
"layer_index": 3,
"directory": "tattoo"
},
{
"layer_index": 4,
"directory": "eye"
}
],
"image_mode": "RGBA"
}