Fix MacOS rpath handling

[abgandar]

To allow both the traditional installation of DACE libraries in system directories and the full in-tree build using FetchContent on MacOSX the logic for RPATH handling is now this:

• build tree: all libraries and binaries are built with full absolute RPATH pointing to the binary tree. This allows any executable linking the dace target to "just run" in place. They are, however, not relocatable
• install tree: all absolute paths are replaced with @rpath to allow relocation and installation into system directories. This allows using find_package() to link DACE programs that are location independent

[abgandar]

In future major releases, we should consider removing the dynamic library option entirely due to the messiness and limited utility (library locations across platforms, C++ library inconsistencies, C++ templates, small size of full library)