Add some long overdue comments.

Author: jan-elastic

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/autoscaling/MlAutoscalingDeciderService.java

@@ -30,6 +30,10 @@
 
 import static org.elasticsearch.core.Strings.format;
 
+/**
+ * This handles ML autoscaling just for classic cloud.
+ * For serverless, see: {@link MlAutoscalingResourceTracker}.
+ */
 public final class MlAutoscalingDeciderService implements AutoscalingDeciderService, LocalNodeMasterListener {
 
     private static final Logger logger = LogManager.getLogger(MlAutoscalingDeciderService.class);

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/autoscaling/MlAutoscalingResourceTracker.java

@@ -48,7 +48,8 @@
 import static org.elasticsearch.xpack.ml.job.JobNodeSelector.AWAITING_LAZY_ASSIGNMENT;
 
 /**
- * backend for new kubernetes based autoscaler.
+ * This handles ML autoscaling just for serverless.
+ * For classic cloud, see: {@link MlAutoscalingDeciderService}.
  */
 public final class MlAutoscalingResourceTracker {
     private static final Logger logger = LogManager.getLogger(MlAutoscalingResourceTracker.class);