Require the caller to pass in the required distros explicitly. This
would allow us to easily add distros in osbuild-pipeline and tests
before exposing them in composer itself, for instance.
This means there is no longer a dependency from the distro package
to each of the individual distros, so the distros are now able
to depend on the distro packag for types and interfaces.
Signed-off-by: Tom Gundersen <teg@jklm.no>
ff0ec01eb6