Be able to support compressed point cloud messages (sensor_msgs/CompressedPointCloud?)

Feature request

Feature description

Lidar point clouds continue to grow and visualizing lidar point in realtime can use a lot of data. Practical amount using for example 4 spinning 128 channel lidars on a vehicle will grow above 1Gb/s.

So I would propose to support some sort of compressed point cloud (gzip:ed, quantization, mpeg-compressed) -> sensor_msgs/CompressedPointCloud.

Some compression ideas:

• GZip, Usually reduces point cloud data size with approximately 50%.
• https://mpeg-pcc.org/index.php/publications/an-overview-of-ongoing-point-cloud-compression-standardization-activities-video-based-v-pcc-and-geometry-based-g-pcc/
• https://cesium.com/blog/2019/02/26/draco-point-clouds/

Implementation considerations

Add a new standard sensor_msgs definition that can be used for compressed point clouds.

Start by reviewing the existing sensor_msgs definitions and the compression approaches linked in the issue. The work is complete when a concrete compressed point cloud message design is agreed and added as a standard sensor_msgs definition, but the format and compression method still need to be determined.