Function handle_pub

async fn handle_pub(
    session: &Session,
    warnings: &mut RouteWarnings,
    out_tx: &Sender<ServerOp>,
    verbose: bool,
    service_id: &str,
    topic: String,
    payload: String,
) -> Result<(), Fatal>

Publishes onto the engine. A bad payload is -ERR Invalid-Message and the session stays up.