Log every use of ILM Move to Step API (elastic#41171)

Usage of the ILM Move to Step API can result in some very odd
situations, and for diagnosing problems arising from these situations it
would be nice to have a record of when this API was called with what
parameters.

Also, adds a dedicated logger for TransportMoveToStepAction, 
rather than using the (deprecated) inherited one.

Author: gwbrown

x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/indexlifecycle/IndexLifecycleRunner.java

@@ -307,6 +307,9 @@ static ClusterState moveClusterStateToStep(String indexName, ClusterState curren
                 "] with policy [" + indexPolicySetting + "] does not exist");
         }
 
+        logger.info("moving index [{}] from [{}] to [{}] in policy [{}]",
+            indexName, currentStepKey, nextStepKey, indexPolicySetting);
+
         return IndexLifecycleRunner.moveClusterStateToNextStep(idxMeta.getIndex(), currentState, currentStepKey,
             nextStepKey, nowSupplier, forcePhaseDefinitionRefresh);
     }

x-pack/plugin/ilm/src/main/java/org/elasticsearch/xpack/indexlifecycle/action/TransportMoveToStepAction.java

@@ -6,6 +6,8 @@
 
 package org.elasticsearch.xpack.indexlifecycle.action;
 
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
 import org.elasticsearch.action.ActionListener;
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.master.TransportMasterNodeAction;
@@ -25,6 +27,8 @@
 import org.elasticsearch.xpack.indexlifecycle.IndexLifecycleService;
 
 public class TransportMoveToStepAction extends TransportMasterNodeAction<Request, Response> {
+    private static final Logger logger = LogManager.getLogger(TransportMoveToStepAction.class);
+
     IndexLifecycleService indexLifecycleService;
     @Inject
     public TransportMoveToStepAction(TransportService transportService, ClusterService clusterService, ThreadPool threadPool,