Fix linkage to octomap(#48)

[aosmw]

With change to use the system liboctomap-dev the liboctomap_rviz_plugins.so does not get proper linkage and so plugin loading fails.

With this change it does.

ldd install/octomap_rviz_plugins/lib/liboctomap_rviz_plugins.so  | grep octo
        liboctomap_msgs__rosidl_typesupport_cpp.so => /opt/ros/humble/lib/liboctomap_msgs__rosidl_typesupport_cpp.so (0x00007fdde6004000)
        liboctomap.so.1.9 => /opt/ros/humble/lib/x86_64-linux-gnu/liboctomap.so.1.9 (0x00007fdde59c2000)
        liboctomath.so.1.9 => /opt/ros/humble/lib/x86_64-linux-gnu/liboctomath.so.1.9 (0x00007fdde35aa000)

[LihanChen2004]

Hi. I am looking forward to this PR being merged and updated in index.ros.org 😢 @wxmerkt