### 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
private String message;
        private long timeout;
        private boolean isRawIndexingData = false;
        StringMessageRequest(String message, long timeout) {
            this(message, timeout, false);
        }
        StringMessageRequest(String message, long timeout, boolean isRawIndexingData) {
            this.message = message;
            this.timeout = timeout;
            this.isRawIndexingData = isRawIndexingData;
        }
        public StringMessageRequest(StreamInput in) throws IOException {
            super(in);
            message = in.readString();
            timeout = in.readLong();
        }
        public StringMessageRequest(String message) {