Function serve_application 

pub async fn serve_application(
    listener: ListenerConfig,
    application: ApplicationFetch,
    max_body_bytes: usize,
    shutdown: CancellationToken,
) -> Result<()>

Bind a TCP listener that forwards every request to an application handler.

This listener is independent of the serverless runtime and can run beside a normal serverful envoy using the same registry shutdown token.