### 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
() -> connectToNode(serviceA, dummy, builder.build())
            );
            assertEquals(ex.getMessage(), "[][" + dummy.getAddress() + "] general node connection failure");
            assertThat(ex.getCause().getMessage(), startsWith("handshake failed"));
            t.join();
        }
    }
    public void testResponseHeadersArePreserved() throws InterruptedException {
        List<String> executors = new ArrayList<>(ThreadPool.THREAD_POOL_TYPES.keySet());
        CollectionUtil.timSort(executors); 
        serviceA.registerRequestHandler("internal:action", ThreadPool.Names.SAME, TestRequest::new, (request, channel, task) -> {
            threadPool.getThreadContext().putTransient("boom", new Object());
            threadPool.getThreadContext().addResponseHeader("foo.bar", "baz");
            if ("fail".equals(request.info)) {
                throw new RuntimeException("boom");
            } else {
                channel.sendResponse(TransportResponse.Empty.INSTANCE);
            }
        });
        CountDownLatch latch = new CountDownLatch(2);
        TransportResponseHandler<TransportResponse> transportResponseHandler = new TransportResponseHandler<TransportResponse>() {
            private final String executor = randomFrom(executors);
            @Override
            public TransportResponse read(StreamInput in) {
                return TransportResponse.Empty.INSTANCE;
            }
            @Override
            public void handleResponse(TransportResponse response) {
                try {
                    assertSame(response, TransportResponse.Empty.INSTANCE);