Add CMake options to install apps or tests for spack builds

At the moment one can optionally build apps (benchmarks) or tests, but not install them.

Most users probably wont ever want to install these, but when installing via spack (package in asc-spack-repo) - especially in the context of containers - one might want to install them to be able to execute them. In spack the build directory is generally removed by spack after installation and in container builds it never leaves the build stage (vs the final stage / container).