### 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
/**
     * This is the number of times that it is not OK to have a master change identity. This many changes or more will be reported as a
     * problem.
     */
    public static final Setting<Integer> IDENTITY_CHANGES_THRESHOLD_SETTING = Setting.intSetting(
        "health.master_history.identity_changes_threshold",
        4,
        0,
        Setting.Property.NodeScope
    );
    public CoordinationDiagnosticsService(
        ClusterService clusterService,
        TransportService transportService,
        Coordinator coordinator,
        MasterHistoryService masterHistoryService
    ) {
        this.clusterService = clusterService;
        this.transportService = transportService;
        this.coordinator = coordinator;
        this.masterHistoryService = masterHistoryService;
        this.nodeHasMasterLookupTimeframe = NODE_HAS_MASTER_LOOKUP_TIMEFRAME_SETTING.get(clusterService.getSettings());
        this.unacceptableNullTransitions = NO_MASTER_TRANSITIONS_THRESHOLD_SETTING.get(clusterService.getSettings());
        this.unacceptableIdentityChanges = IDENTITY_CHANGES_THRESHOLD_SETTING.get(clusterService.getSettings());
    }
    /**
     * This method completes the initialization of the CoordinationDiagnosticsService. It kicks off polling for remote master stability
     * results on non-master-eligible nodes, and registers the service as a cluster service listener on all nodes.
     */
    public void start() {
        /*