### 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`)
test/framework/src/main/java/org/elasticsearch/transport/AbstractSimpleTransportTestCase.java
AtomicInteger requestsReceived = new AtomicInteger();
            AtomicInteger requestsSent = new AtomicInteger();
            AtomicInteger responseReceived = new AtomicInteger();
            AtomicInteger responseSent = new AtomicInteger();
            @Override
            public void onRequestReceived(long requestId, String action) {
                if (action.equals(ACTION)) {
                    requestsReceived.incrementAndGet();
                }
            }
            @Override
            public void onResponseSent(long requestId, String action, TransportResponse response) {
                if (action.equals(ACTION)) {
                    responseSent.incrementAndGet();
                }
            }
            @Override
            public void onResponseSent(long requestId, String action, Exception error) {
                if (action.equals(ACTION)) {
                    responseSent.incrementAndGet();
                }
            }
            @Override
            @SuppressWarnings("rawtypes")
            public void onResponseReceived(long requestId, Transport.ResponseContext context) {
                if (context.action().equals(ACTION)) {