Add an unit test to verify that the `describe` command can describe all
image types. I've recently ran into issue when describing ostree-based
and `*-simplified-installer` image types.
Add new dependecy for working with YAML - sigs.k8s.io/yaml.
This is what we will probably converge to, since our currently used YAML
library is unmaintained.
Signed-off-by: Tomáš Hozza <thozza@redhat.com>