Fixed NamespacedMetricExt.getGauge to effectively return the Gauge metric instance stored in the metric store.

Author: andsel

logstash-core/src/main/java/org/logstash/instrument/metrics/NamespacedMetricExt.java

@@ -76,7 +76,7 @@ protected IRubyObject getCounter(final ThreadContext context, final IRubyObject
     @Override
     protected IRubyObject getGauge(final ThreadContext context, final IRubyObject key,
         final IRubyObject value) {
-//        return metric.gauge(context, namespaceName, key, value);
+        metric.gauge(context, namespaceName, key, value);
         return collector(context).callMethod(
                 context, "get", new IRubyObject[]{namespaceName, key, MetricExt.GAUGE}
         );