control plane > add comment for using Gauge instead of counter

Author: DC2-DanielKrueger

hivemq-edge/src/main/java/com/hivemq/protocols/ProtocolAdapterMetrics.java

@@ -14,6 +14,8 @@
 public class ProtocolAdapterMetrics {
 
     private final @NotNull MetricRegistry metricRegistry;
+    // we use this AtomicInteger in order to have a gauge for the current amount of adapters to
+    // be consistent with the other metrics
     private final AtomicInteger currentAdapters = new AtomicInteger();
 
     @Inject