Simplify the Actuator's hypermedia support

This commit replaces the Acuator's support for hypermedia with a
single endpoint that returns HAL-formatted links to all of the
available endpoints. This is done without requiring Spring HATEOAS
to be on the classpath in a similar manner to the existing
CloudFoundry discovery endpoint.

Closes gh-9901

spring-boot-samples/spring-boot-sample-actuator/pom.xml

@@ -28,10 +28,10 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-web</artifactId>
 		</dependency>
-		<dependency>
+		<!-- <dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-security</artifactId>
-		</dependency>
+		</dependency> -->
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-jdbc</artifactId>