Since we were only testing x86_64 and aarch64, the manifests for ppc64le
and s390x were never being generated in CI.
Adding new jobs, generated by the same configure-generators script, that
just generate these manifests in a new type of child pipeline:
generate-manifests-{distro}-{arch}.
These jobs all run on x86_64, but we separate them per distro-arch so
they can run in parallel.  The goal is to ensure that at least the
manifest generation works for these architectures and the package sets
resolve, even if we don't test that they actually build.

powerpc-utils and s390utils-base require /usr/bin/perl