image_transport::CameraPublisher does not support cv::Mat Type adapter

[Yadunund]

PR ros-perception/vision_opencv#441 introduced a type adapter between cv::Mat and Image msg.

It would be great if the image_transport::CameraPublisher also supported publishing with this type adapter. I'm happy to work on this feature if no one else is already working on it.

I can add an overloaded function here to publish a unique_ptr of the adapter. Subsequently also change the publisher in the Impl class to a type adapted one.

This would enable users to setup ImagePublishers that supports type adaptation internally.