### 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
final ExecutionException e = expectThrows(ExecutionException.class, res::get);
        Throwable cause = ExceptionsHelper.unwrapCause(e.getCause());
        assertThat(cause, instanceOf(ConnectTransportException.class));
        assertThat(cause.getMessage(), allOf(containsString(nodeA.getName()), containsString(nodeA.getAddress().toString())));
        
        assertBusy(() -> assertFalse(serviceB.nodeConnected(nodeA)));
        
        expectThrows(ConnectTransportException.class, () -> connectToNode(serviceB, nodeA));
        expectThrows(ConnectTransportException.class, () -> openConnection(serviceB, nodeA, TestProfiles.LIGHT_PROFILE));
    }
    public void testMockUnresponsiveRule() throws InterruptedException {
        serviceA.registerRequestHandler(
            "internal:sayHello",
            ThreadPool.Names.GENERIC,
            StringMessageRequest::new,
            (request, channel, task) -> {
                assertThat("moshe", equalTo(request.message));
                throw new RuntimeException("bad message !!!");
            }
        );
        serviceB.addUnresponsiveRule(serviceA);
        Future<StringMessageResponse> res = submitRequest(
            serviceB,
            nodeA,
            "internal:sayHello",
            new StringMessageRequest("moshe"),
            TransportRequestOptions.timeout(HUNDRED_MS),
            new TransportResponseHandler<StringMessageResponse>() {
                @Override
                public StringMessageResponse read(StreamInput in) throws IOException {