adding license header to cached supplier

Author: benwtrent

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/ml/utils/CachedSupplier.java

@@ -1,3 +1,8 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License;
+ * you may not use this file except in compliance with the Elastic License.
+ */
 package org.elasticsearch.xpack.core.ml.utils;
 
 import java.util.function.Supplier;