Function start_server_ext 

pub async fn start_server_ext(
    config: impl Into<ServerConfigHolder>,
    tls_identity: Option<TlsIdentity>,
    registry: Arc<PeerRegistry>,
    event_tx: Option<Sender<ServerTransferEvent>>,
    download_manager: Option<Arc<DownloadManager>>,
    dufs_manager: Option<Arc<DufsManager>>,
) -> Result<ServerHandle>

Extended server launcher permitting injected download and dufs managers.