fixes #7234 - add foreman-release-scl meta-package

Depends on the release RPMs from softwarecollections.org, for RHEL clone users
to get the repositories that provide RHSCL rebuilds.

extras/ will be consumed by the mash split script when we build repos, much
like comps/.  These files will be fetched and included into the finished repo.

(cherry picked from commit ec9bce9e791635c92962c0fff81986698fc5cb77)
Release 1.6.1
Automatic commit of package [foreman] minor release [1.6.1-1].
Automatic commit of package [foreman-proxy] minor release [1.6.1-1].
Automatic commit of package [foreman-selinux] minor release [1.6.1-1].