Make Elasticsearch dependency available to javadoc generation

See gh-12600

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

@@ -492,6 +492,11 @@
 			<artifactId>http2-server</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.elasticsearch.client</groupId>
+			<artifactId>elasticsearch-rest-high-level-client</artifactId>
+			<version>${elasticsearch.version}</version>
+		</dependency>
 		<dependency>
 			<groupId>org.flywaydb</groupId>
 			<artifactId>flyway-core</artifactId>