Add dh_shlibdeps entry for libraries installed by ament_vendor

[cottsay]

It seems that dh_shlibdeps needs to know about each location where shared object libraries are installed so that it knows which libraries are provided by a package. This is particularly important information in the context of multiple inter-linked libraries within a single package.

The ament_vendor macro provided by ament_cmake_vendor_package installs to the opt/{package_name} sub-tree, so we should search for dynamic libraries there as well.

https://man7.org/linux/man-pages/man1/dh_shlibdeps.1.html

[cottsay]

This should unblock the gazebo vendoring and eliminate the rviz_ogre_vendor patches we apply today.

[cottsay]

(maybe not the entire rviz_ogre_vendor patch, but I'm skeptical that the plugins in the OGRE subdirectory need to be part of this).

[azeey]

I've tested this locally with gz_dartsim_vendor and it worked great! Thanks @cottsay