Feature request: API endpoint to generate only control images

[kft334]

I need an endpoint to generate only control images for my app.

Intended use (Photo-bashing with ControlNet Objects):

1. Crop a section of an image. (Generated or not)
2. Remove the background of the cropped image.
3. Paste the matted cropped section on a black image.
4. Generate the control image from the cropped single-object image.
5. Set all black pixels transparent in the control image to create an object control stamp.
6. Use many stamps to compose new control images for use with ControlNet.