Ability to add other channels (RGB etc.) when generating the PointCloud2 msgs

[garyedwards]

Is your feature request related to a problem? Please describe.
We are creating registered RGB and IR images in the same frame as those produced by our Ousters. We would like to add this data to the PointCloud2 msgs that are produced by the driver for use downstream.

Describe the solution you'd like
The driver to be able to subscribe to additional images and add their data to the generated PointCloud2 msgs.

Describe alternatives you've considered
We have considered using point_cloud_xyzrgb from depth_image_proc but do not have the appropriate calibration info for the Ousters (not sure a relevant config could be generated?). Also this only supports adding a single extra channel.

If there are other methods of integrating additional channels like colour I would be very interested in exploring these alternatives.

Targeted Platform (please complete the following information only if applicable, otherwise dot N/A):

• Ouster Sensor? N/A
• Ouster Firmware Version? N/A
• ROS version/distro? ROS1 (initially) and ROS2 support
• Operating System? N/A
• Machine Architecture? X68_64 and ARM