### 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
assertTrue(threadPool.getThreadContext().getResponseHeaders().containsKey("foo.bar"));
                    assertEquals(1, threadPool.getThreadContext().getResponseHeaders().get("foo.bar").size());
                    assertEquals("baz", threadPool.getThreadContext().getResponseHeaders().get("foo.bar").get(0));
                    assertNull(threadPool.getThreadContext().getTransient("boom"));
                } finally {
                    latch.countDown();
                }
            }
            @Override
            public void handleException(TransportException exp) {
                try {
                    assertTrue(threadPool.getThreadContext().getResponseHeaders().containsKey("foo.bar"));
                    assertEquals(1, threadPool.getThreadContext().getResponseHeaders().get("foo.bar").size());
                    assertEquals("baz", threadPool.getThreadContext().getResponseHeaders().get("foo.bar").get(0));
                    assertNull(threadPool.getThreadContext().getTransient("boom"));
                } finally {
                    latch.countDown();
                }
            }
            @Override
            public String executor() {
                return executor;
            }
        };
        serviceB.sendRequest(nodeA, "internal:action", new TestRequest(randomFrom("fail", "pass")), transportResponseHandler);
        serviceA.sendRequest(nodeA, "internal:action", new TestRequest(randomFrom("fail", "pass")), transportResponseHandler);
        latch.await();
    }
    public void testHandlerIsInvokedOnConnectionClose() throws IOException, InterruptedException {
        List<String> executors = new ArrayList<>(ThreadPool.THREAD_POOL_TYPES.keySet());