### 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`)
server/src/main/java/org/elasticsearch/cluster/coordination/CoordinationDiagnosticsService.java
* As mentioned in the comment in cancelPollingClusterFormationInfo(), there is a slim possibility here that we will
                     * add a task here for a poll that has already been cancelled. But when it completes and runs
                     * rescheduleClusterFormationFetchConsumer() we will then see that clusterFormationInfoTasks does not equal
                     * cancellables, so it will not be run again.
                     */
                    try {
                        cancellables.put(
                            masterEligibleNode,
                            fetchClusterFormationInfo(
                                masterEligibleNode,
                                responseConsumer.andThen(
                                    rescheduleClusterFormationFetchConsumer(masterEligibleNode, responseConsumer, cancellables)
                                )
                            )
                        );
                    } catch (EsRejectedExecutionException e) {
                        if (e.isExecutorShutdown()) {
                            logger.trace("Not rescheduling request for cluster coordination info because this node is being shutdown", e);
                        } else {
                            throw e;
                        }
                    }
                } else {
                    cancellables.values().forEach(Scheduler.Cancellable::cancel);
                }
            } else {
                cancellables.values().forEach(Scheduler.Cancellable::cancel);
            }
        };
    }