Added a CMake version check and (optional) OpenMP propagation in blasppConfig.cmake.in

Generally, full propagation of dependencies should be handled by CMake Config files, i.e.

When use_openmp is enabled in the CMake build system, OpenMP discovery is not propagated in the Config file. These changes check for the dependency ( find_dependency vs find_package which propagates things like REQUIRED and QUIET to that discovery invocation) such that the end user doesn’t need to find it themselves.