Separate check for pybind11 and pybind11_json system-wide installation.
The pybind11 and pybind11_json are separate packages that come with their own CMake config files.
The current implementation check whether pybind11 is installed system-wide. If yes, then it uses the system-wide pybind11 and pybind11_json. If not, then it uses our internal submodule.
The problem is that pybind11 and pybind11_json are separate packages. There are situations when pybind11 is installed system-wide and pybind11_json is not. In this case, labRemote will fail to build.
This MR fixes it by independently deciding whether to use an external or internal pybind11_json.