Function serve 

async fn serve<Client>(
    bind: &str,
    fhir_client: Arc<Client>,
    config: Arc<ReceiverConfig>,
    max_connections: usize,
) -> Result<(), OperationOutcomeError>
where
    Client: FHIRClient<(), OperationOutcomeError> + Send + Sync + 'static,

Accepts connections until shutdown is signalled.