Re-enable ros_gz_point_cloud

[mjcarroll]

The point cloud plugin quite some time ago, but still has a lot of utility. The context for originally disabling is here: #40

[mjcarroll]

CC: @bperseghetti

[SuperJappie08]

I attempted to port this for ROS Jazzy and Gazebo Harmonic. (Because it looked useful and doable, and I wanted more about Gazebo)

However, even after converting it to a rendering plugin, the performance improvements gazebosim/gz-sensors#447 and gazebosim/gz-sensors#413, it is no longer possible to get data via the renderer directly without subscribing to the (gazebo) topic.
(Unless there is a way to retrieve and attach to the gz::sensor object directly, which I was unable to find)

(My branch lives here, although not functioning as expected SuperJappie08/ros_gz jazzy-point-cloud)