### 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
public void testNotifyOnShutdown() throws Exception {
        final CountDownLatch latch2 = new CountDownLatch(1);
        final CountDownLatch latch3 = new CountDownLatch(1);
        try {
            serviceA.registerRequestHandler(
                "internal:foobar",
                ThreadPool.Names.GENERIC,
                StringMessageRequest::new,
                (request, channel, task) -> {
                    try {
                        latch2.await();
                        logger.info("Stop ServiceB now");
                        serviceB.stop();
                    } catch (Exception e) {
                        fail(e.getMessage());
                    } finally {
                        latch3.countDown();
                    }
                }
            );
            Future<TransportResponse.Empty> foobar = submitRequest(
                serviceB,
                nodeA,
                "internal:foobar",
                new StringMessageRequest(""),
                EmptyTransportResponseHandler.INSTANCE_SAME
            );
            latch2.countDown();
            assertThat(expectThrows(ExecutionException.class, foobar::get).getCause(), instanceOf(TransportException.class));
            latch3.await();