[Feature Request] Basic shapes/vector based masking.

Hello. I've noticed that ComfyUI is able to create bitmap masks by right clicking on an image and selecting MaskEditor, which is great on itself.

But then i noticed the mask is loaded as a separate .png file and it is not embeded together with saved output, i guess that makes sense because embedding a full png file inside another will bloat up the output size.

So i would like to suggest a embeddable vector based masking. At the very least, basic shapes like rectangles and eclipse would be a good start but implementing freeform vector pen would be great.

For reference, with automatic1111 webgui, this is made possible with [this script](https://github.com/dfaker/stable-diffusion-webui-cv2-external-masking-script).

It would be great if we have a similar feature in ComfyUI as this will minimize switching between different app and it will also improve the workflow reproducability by embedding the mask metadata together with the output.

Thanks!