The original Koji implementation expected that the output of a content
generator is only an image. While in reality, we will eventually upload
other types of files as outputs to Koji, such as logs and osbuild
manifest.
Rename Koji structures and their members to better map to the upstream
Koji documentation and their JSON representation. Add comments to
structures. Define type aliases and constants for string values which
are more like enums, than a free-form values.
These changes have no effect on the actual JSON representation of any of
the structures
Signed-off-by: Tomáš Hozza <thozza@redhat.com>