Function do_upgrade 

pub(crate) async fn do_upgrade(
    storage: &Storage,
    booted_cfs: &BootedComposefs,
    host: &Host,
    imgref: &ImageReference,
    img_manifest_config: &ImgConfigManifest,
    opts: &DoUpgradeOpts,
) -> Result<()>

Performs the Update or Switch operation