Update Rawhide config to build a modular variant
    
    This should cause the compose to contain all the previous content plus a
    separate Modular variant with packages specified by list of modules in
    variants file.
    
    The final layout of the compose should be like this:
    
        compose/Everything/$arch/os/
        compose/Modular/$arch/os/
    
    Relates: https://pagure.io/releng/issue/7227
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>