### Description

The `sendRequest` method is asynchronous and notifies a 
`TransportResponseHandler` when it completes the excecution
(successfully or unsuccessfully). 

When opening the connection we only catch `NodeNotConnectedException`
( https://github.com/elastic/elasticsearch/blob/main/server/src/main/java/org/elasticsearch/transport/TransportService.java#L719 ) which is currently fine as no implementations
throw other type of exception however, it'd be best to catch `Exception` here
so the `handler` gets notified of potential exceptions (as opposed to the caller
having to `try/catch` the call to `sendRequest`)
server/src/main/java/org/elasticsearch/transport/TransportService.java
private final List<TransportMessageListener> listeners = new CopyOnWriteArrayList<>();
        @Override
        public void onRequestReceived(long requestId, String action) {
            for (TransportMessageListener listener : listeners) {
                listener.onRequestReceived(requestId, action);
            }
        }
        @Override
        public void onResponseSent(long requestId, String action, TransportResponse response) {
            for (TransportMessageListener listener : listeners) {
                listener.onResponseSent(requestId, action, response);
            }
        }
        @Override
        public void onResponseSent(long requestId, String action, Exception error) {
            for (TransportMessageListener listener : listeners) {