opencv compatability - "use legacy camera support"

[petercwallis]

It turns out opencv can't open the default camera on the pi, and this is a known issue (opencv's) but they are having trouble:
opencv/opencv#21653

It looks like they are a fair way along, but are suffering from "churn". Just thought I'd point this out just in case someone working on rpicam-apps might like to take a look and possibly help.

[naushir]

Thanks for pointing it out. I'm afraid integrating libcamera support directly into OpenCV is not down to us. However, we do have examples in both rpicam-apps and Picamera2 that integrate image postprocessing using OpenCV if that helps your use case.