### 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
* Returns the health result for the case when we have seen a master recently (at some point in the last 30 seconds).
     * @param localMasterHistory The master history as seen from the local machine
     * @param explain Whether to calculate and include the details and user actions in the result
     * @return The CoordinationDiagnosticsResult for the given localMasterHistory
     */
    private CoordinationDiagnosticsResult diagnoseOnHaveSeenMasterRecently(MasterHistory localMasterHistory, boolean explain) {
        int masterChanges = MasterHistory.getNumberOfMasterIdentityChanges(localMasterHistory.getNodes());
        logger.trace(
            "Have seen a master in the last {}): {}",
            nodeHasMasterLookupTimeframe,
            localMasterHistory.getMostRecentNonNullMaster()
        );
        final CoordinationDiagnosticsResult result;
        if (masterChanges >= unacceptableIdentityChanges) {
            result = diagnoseOnMasterHasChangedIdentity(localMasterHistory, masterChanges, explain);
        } else if (localMasterHistory.hasMasterGoneNullAtLeastNTimes(unacceptableNullTransitions)) {
            result = diagnoseOnMasterHasFlappedNull(localMasterHistory, explain);
        } else {
            result = getMasterIsStableResult(explain, localMasterHistory);
        }
        return result;
    }
    /**
     * Returns the health result when we have detected locally that the master has changed identity repeatedly (by default more than 3
     * times in the last 30 minutes)
     * @param localMasterHistory The master history as seen from the local machine
     * @param masterChanges The number of times that the local machine has seen the master identity change in the last 30 minutes
     * @param explain Whether to calculate and include the details in the result
     * @return The CoordinationDiagnosticsResult for the given localMasterHistory
     */