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>