Function run 

pub async fn run(
    addr: &str,
    kg: Arc<GraphHandle>,
    auth_token: Option<Arc<str>>,
    tls_cert: Option<PathBuf>,
    tls_key: Option<PathBuf>,
) -> Result<()>

Bind addr and serve the HTTP transport until the process is killed.

When tls_cert and tls_key are both set, the transport is served over TLS (HTTPS); otherwise it stays plaintext. The caller (config.rs) guarantees the two are set together.