Use standard location to install CMake files

[fbridault]

While packaging camp for Debian, it has been noticed that we do not install the camp files on the standard location. We install it in /usr/lib/camp/cmake this should be rather /usr/lib/cmake/camp. Also we should use the variable CMAKE_INSTALL_LIBDIR instead of lib to handle multi-arch paths gracefully and automatically.

[fbridault]

The patch provided here https://salsa.debian.org/med-team/camp/-/blob/master/debian/patches/fix_cmake_target.patch should make the job.