osbuild: support specifying upload_options
    
    Since version 9, the `koji-osbuild` plugin supports specifying upload
    options as part of a Koji build. This enables one to upload the built
    image directly to the cloud environment as part of the image build in
    Koji.
    
    Extend the configuration schema with `upload_options`.
    Extend the documentation and describe valid `upload_options` values.
    Add a unit test testing a scenario when `upload_options` are specified.
    
    Signed-off-by: Tomas Hozza <thozza@redhat.com>