Publish CompressedImage from usb_cam

[hello-amal]

Currently, usb_cam only supports Image types. It would be great if it could instead/also publish a CompressedImage.

Doing so it quite straightforward: cv_bridge has functions to convert an OpenCV image to a CompressedImage message (used in the web interface here). I'd suggest adding a parameter, compress_image, that will essentially append /compressed to publish_topic and publish the image as a CompressedImage.