Add %pyproject_save_files macro
    
    This macro save generates file section to %pyproject_files. It should
    simplify %files section and allow to build by some automatic machinery
    
    Supposed use case in Fedora:
        %install
        %pyproject_install
        %pyproject_save_files requests _requests
    
        %files -n python3-requests -f %{pyproject_files}
        %doc README.rst
        %license LICENSE
    
    Automatic build of arbitrary packages (e.g. in Copr):
        %install
        %pyproject_install
        %pyproject_save_files * +bindir // save all modules with executables
    
        %files -n python3-requests -f %{pyproject_files}
    
    Co-Authored-By: Miro Hrončok <miro@hroncok.cz>