[ML] Remove excessive logging from ML upgrade mode (#65897)

While looking into another issue I noticed that
when enabling or disabling ML upgrade mode some
very low level messages are logged at the INFO
level.  This commit reduces that to TRACE.

x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/action/TransportSetUpgradeModeAction.java

@@ -229,13 +229,13 @@ protected void masterOperation(Task task, SetUpgradeModeAction.Request request,
 
                 @Override
                 protected AcknowledgedResponse newResponse(boolean acknowledged) {
-                    logger.info("Cluster update response built: " + acknowledged);
+                    logger.trace("Cluster update response built: " + acknowledged);
                     return AcknowledgedResponse.of(acknowledged);
                 }
 
                 @Override
                 public ClusterState execute(ClusterState currentState) throws Exception {
-                    logger.info("Executing cluster state update");
+                    logger.trace("Executing cluster state update");
                     MlMetadata.Builder builder = new MlMetadata.Builder(currentState.metadata().custom(MlMetadata.TYPE));
                     builder.isUpgradeMode(request.isEnabled());
                     ClusterState.Builder newState = ClusterState.builder(currentState);