Add fedora compose ostree repo to fedora-repos-ostree subpackage
This will allow community members to more easily test development
builds because the remote information for the compose ostree repo
will already be on the system. That means they'll be a simple
`rpm-ostree rebase fedora-compose:<ref>` away from testing out a
development version.
Signed-off-by: Dusty Mabe <dusty@dustymabe.com>