Add package info to o.s.b.autoconfigure.elasticsearch.rest

Closes gh-22147

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/elasticsearch/rest/package-info.java

+/*
+ * Copyright 2012-2020 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * Deprecated auto-configuration for Elasticsearch client, superseded by classes in
+ * {@code org.springframework.boot.autoconfigure.elasticsearch}.
+ */
+package org.springframework.boot.autoconfigure.elasticsearch.rest;