public void logValue(String key, String value) {
            traceNode.add(new TraceNode(new LogValue(key, value), 0));
        }
Adds a key-value which will be logged to the access log of this request.
Multiple values may be set to the same key. A value cannot be removed once set,
but it can be overwritten by adding another value for the same key.
container-core/src/main/java/com/yahoo/processing/execution/Execution.java