Update documentation on Actuator hypermedia support

Spring Boot Actuator hypermedia support has been disabled by default via
c7c685f6, but its documentation wasn't updated.

This commit updates the documentation related to the change.

See gh-7215

spring-boot-actuator-docs/pom.xml

@@ -44,6 +44,11 @@
 			<artifactId>h2</artifactId>
 			<scope>provided</scope>
 		</dependency>
+		<dependency>
+			<groupId>com.jayway.jsonpath</groupId>
+			<artifactId>json-path</artifactId>
+			<scope>provided</scope>
+		</dependency>
 		<dependency>
 			<groupId>junit</groupId>
 			<artifactId>junit</artifactId>
@@ -82,6 +87,10 @@
 			<groupId>org.springframework.hateoas</groupId>
 			<artifactId>spring-hateoas</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.plugin</groupId>
+			<artifactId>spring-plugin-core</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.springframework.restdocs</groupId>
 			<artifactId>spring-restdocs-mockmvc</artifactId>

spring-boot-actuator-docs/src/main/asciidoc/index.adoc

@@ -58,7 +58,7 @@ HAL browser is not active).
 
 == Hypermedia Support
 If https://projects.spring.io/spring-hateoas[Spring HATEOAS] is enabled  (i.e. if it is
-on the classpath by default) then the Actuator endpoint responses are enhanced with
+on the classpath by default) and `endpoints.hypermedia.enabled` is set to `true` then the Actuator endpoint responses are enhanced with
 hypermedia in the form of "links". The default media type for responses is
 http://stateless.co/hal_specification.html[HAL], resulting in each resource having an
 extra property called "_links". You can change the media type to another one supported by

spring-boot-actuator-docs/src/restdoc/java/org/springframework/boot/actuate/hypermedia/HypermediaEndpointDocumentation.java

@@ -33,12 +33,13 @@ import org.springframework.test.web.servlet.MockMvc;
 
 import static org.springframework.restdocs.mockmvc.MockMvcRestDocumentation.document;
 import static org.springframework.test.web.servlet.request.MockMvcRequestBuilders.get;
+import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.status;
 
 @RunWith(SpringRunner.class)
 @ContextConfiguration(classes = SpringBootHypermediaApplication.class, loader = SpringBootContextLoader.class)
 @WebAppConfiguration
-@TestPropertySource(properties = "spring.jackson.serialization.indent_output=true")
+@TestPropertySource(properties = { "spring.jackson.serialization.indent_output=true", "endpoints.hypermedia.enabled=true" })
 @DirtiesContext
 @AutoConfigureMockMvc
 @AutoConfigureRestDocs("target/generated-snippets")
@@ -56,7 +57,9 @@ public class HypermediaEndpointDocumentation {
 	@Test
 	public void metrics() throws Exception {
 		this.mockMvc.perform(get("/metrics").accept(MediaType.APPLICATION_JSON))
-				.andExpect(status().isOk()).andDo(document("metrics/hypermedia"));
+				.andExpect(status().isOk())
+				.andExpect(jsonPath("$._links.self.href").value("http://localhost:8080/metrics"))
+				.andDo(document("metrics/hypermedia"));
 	}
 
 	@Test

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -930,6 +930,7 @@ content into your application; rather pick only the properties that you need.
 	# ENDPOINTS ({sc-spring-boot-actuator}/endpoint/AbstractEndpoint.{sc-ext}[AbstractEndpoint] subclasses)
 	endpoints.enabled=true # Enable endpoints.
 	endpoints.sensitive= # Default endpoint sensitive setting.
+	endpoints.hypermedia.enabled=false # Enable hypermedia support for endpoints.
 	endpoints.actuator.enabled=true # Enable the endpoint.
 	endpoints.actuator.path= # Endpoint URL path.
 	endpoints.actuator.sensitive=false # Enable security on the endpoint.

spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -205,7 +205,7 @@ For example, to mark _all_ endpoints as sensitive except `info`:
 === Hypermedia for actuator MVC endpoints
 If http://projects.spring.io/spring-hateoas[Spring HATEOAS] is on the classpath (e.g.
 through the `spring-boot-starter-hateoas` or if you are using
-http://projects.spring.io/spring-data-rest[Spring Data REST]) then the HTTP endpoints
+http://projects.spring.io/spring-data-rest[Spring Data REST]) and `endpoints.hypermedia.enabled` is set to `true` then the HTTP endpoints
 from the Actuator are enhanced with hypermedia links, and a "`discovery page`" is added
 with links to all the endpoints. The "`discovery page`" is available on `/actuator` by
 default. It is implemented as an endpoint, allowing properties to be used to configure