Add user-friendly topic for pointcloud

[whoenig]

Using ros2 echo pointCloud doesn't provide any useful information. For cases where it is helpful to have the numerical values of individual markers, it would be helpful to have a topic with a simple pointarray.

[whoenig]

See IMRCLab/crazyswarm2#188. Another option is to write a simple node that subscribes to /pointCloud and outputs the points in a user-friendly format.