Add support for `lhcbproject.json` metadata file
The advantages of using lhcbproject.json instead of lhcbproject.yml is that JSON does not require external Python modules and that CMake (3.19) has builtin JSON support.
The advantages of using lhcbproject.json instead of lhcbproject.yml is that JSON does not require external Python modules and that CMake (3.19) has builtin JSON support.