Allow Setting CMAKE_CXX_STANDARD via Command Line in CMake

[raghunandannm]

We at openPASS are planning to update protobuf to 3.22.0 or higher. However, for these versions of protobuf CMAKE_CXX_STANDARD 14 is required. But the CMAKELISTS.txt in open-simulation-interface hard-coded the CMAKE_CXX_STANDARD to 11. Therefore, it would be great if we there is an optional feature which also allows the user to set the CMAKE_CXX_STANDARD through command line.