Auto-configure Elasticsearch REST clients

This commit adds auto-configuration support for both `RestClient` and
`RestHighLevelClient` which are provided by `elasticsearch-rest-client`
and `elasticsearch-rest-high-level-client` dependencies respectively.

`RestClient` is associated with configuration properties in the
`spring.elasticsearch.rest.*` namespace, since this is the component
taking care of HTTP communication with the actual Elasticsearch node.

`RestHighLevelClient` wraps the first one and naturally inherits that
configuration.

Closes gh-12600

spring-boot-project/spring-boot-dependencies/pom.xml

@@ -1757,6 +1757,16 @@
 				<artifactId>transport-netty4-client</artifactId>
 				<version>${elasticsearch.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.elasticsearch.client</groupId>
+				<artifactId>elasticsearch-rest-client</artifactId>
+				<version>${elasticsearch.version}</version>
+			</dependency>
+			<dependency>
+				<groupId>org.elasticsearch.client</groupId>
+				<artifactId>elasticsearch-rest-high-level-client</artifactId>
+				<version>${elasticsearch.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.firebirdsql.jdbc</groupId>
 				<artifactId>jaybird-jdk17</artifactId>