Fix link elements in restdoc headings

Replace `Link :` prefixes in the restdoc headings with link icons next
to the HTTP request. This fixes render issues with the titles and allows
the TOC to still function correctly.

Fixes gh-3689

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

-=== Link: autoconfig
+=== /autoconfig
 This endpoint is a report on the Spring Boot auto-configuration process that happened when
 your application started up. It lists all the  `@Conditional` annotations that were
 evaluated as the context started and in each case it gives an indication of if (and why)
@@ -16,7 +16,7 @@ of overlap.
 Example curl request:
 include::{generated}/autoconfig/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../autoconfig[icon:external-link[role="silver"]]##
 include::{generated}/autoconfig/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: beans
+=== /beans
 This endpoint is a report on the Spring Boot `ApplicationContext`. It lists the beans in
 the context and their dependencies, detailing the names and concrete classes of each bean.
 
@@ -7,7 +7,7 @@ NOTE: Some beans are pure configuration (any class that is annotated `@Configura
 Example curl request:
 include::{generated}/beans/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../beans[icon:external-link[role="silver"]]##
 include::{generated}/beans/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: configprops
+=== /configprops
 This endpoint is a report on the Spring Boot `@ConfigurationProperties` beans. Beans with
 this annotation are bound to the `Environment` on startup, so they reflect the
 externalised configuration of the application. Beans are listed by name. A bean that is
@@ -9,7 +9,7 @@ specified in the  `@ConfigurationProperties` annotation.
 Example curl request:
 include::{generated}/configprops/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../configprops[icon:external-link[role="silver"]]##
 include::{generated}/configprops/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: dump
+=== /dump
 This endpoint is a thread dump: the result is a list of threads each with their name,
 monitor state and stack. It is the same information as you would get from `kill -3` of a
 running Java process. It can be very useful for detecting issues at runtime, especially
@@ -10,7 +10,7 @@ NOTE: Some `SecurityManager` implementations might prevent this endpoint from wo
 Example curl request:
 include::{generated}/dump/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../dump[icon:external-link[role="silver"]]##
 include::{generated}/dump/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: env
+=== /env
 This endpoint is a dump of the Spring `Environment`. It lists the active profiles and all
 the `PropertySources` in the `Environment` (the ones that are listed first take precedence
 when binding to `@ConfigurationProperties` or `@Value`). Normally you will see the Java
@@ -8,7 +8,7 @@ any `.properties` or `.yml` files used to configure the application on start up.
 Example curl request:
 include::{generated}/env/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../env[icon:external-link[role="silver"]]##
 include::{generated}/env/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: health
+=== /health
 This endpoint is an indication of the health of the application. It has an overall status
 ("UP", "DOWN" etc.), which is the only thing you see unless either you are authenticated
 or the endpoint is marked as `sensitive=false` (`endpoints.health.sensitive=false`).
@@ -10,7 +10,7 @@ The HTTP code in the response reflects the status (e.g. "`UP`"=200,
 Example curl request:
 include::{generated}/health/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../health[icon:external-link[role="silver"]]##
 include::{generated}/health/http-request.adoc[]
 
 Example HTTP response:

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

 = Spring Boot Actuator Endpoints
 :toc: left
 :idprefix: spring_boot_actuator_
+:sectanchors:
+:icons: font
+:last-update-label!:
 
 Actuator endpoints allow you to monitor and interact with your application. Spring Boot
 includes a number of built-in endpoints and you can also add your own. For example the
@@ -17,7 +20,7 @@ include::{generated}/endpoints.adoc[]
 
 
 
-=== Link: logfile
+=== /logfile
 This endpoint (if available) contains the plain text logfile configured by the user
 using `logging.file` or `logging.path` (by default logs are only emitted on stdout
 so one of these properties has to be set for this endpoint to be active).
@@ -25,7 +28,7 @@ so one of these properties has to be set for this endpoint to be active).
 Example curl request:
 include::{generated}/logfile/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../logfile[icon:external-link[role="silver"]]##
 include::{generated}/logfile/http-request.adoc[]
 
 Example HTTP response:
@@ -33,7 +36,7 @@ include::{generated}/logfile/http-response.adoc[]
 
 
 
-=== Link: docs
+=== /docs
 This endpoint (if available) contains HTML documemtation for the other endpoints. Its path
 can be "/docs" (if there is an existing home page) or "/" (otherwise, including if the
 HAL browser is not active).

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

-=== Link: info
+=== /info
 This endpoint is empty and marked as `sensitive=false` by default (so it is
 unauthenticated by default if Spring Security is in use). It reflects the content of the
 `info.*` properties  in the `Environment`, as well as the properties in `git.properties`
@@ -7,7 +7,7 @@ if such a file exists in the root of the classpath.
 Example curl request:
 include::{generated}/info/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../info[icon:external-link[role="silver"]]##
 include::{generated}/info/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: mappings
+=== /mappings
 This endpoint lists the Spring MVC request mappings, so users can see the handlers
 registered for requests by path, method, media type, etc.
 
 Example curl request:
 include::{generated}/mappings/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../mappings[icon:external-link[role="silver"]]##
 include::{generated}/mappings/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: metrics
+=== /metrics
 This endpoint lists the public metrics exposed by the application. By default this
 includes all the counters in the `CounterService` and all the gauges in the
 `GaugeService`, plus a few JVM metrics about memory and uptime. Users can register
@@ -8,7 +8,7 @@ counters and gauges.
 Example curl request:
 include::{generated}/metrics/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../metrics[icon:external-link[role="silver"]]##
 include::{generated}/metrics/http-request.adoc[]
 
 Example HTTP response:

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

-=== Link: trace
+=== /trace
 This endpoint lists contents of the `TraceRepository` (which users can override by
 providing a bean of that type, or by injecting that bean and adding stuff to it). By
 default it stores the last 100 HTTP requests, including all headers in the request and
@@ -7,7 +7,7 @@ response, and the path and HTTP status.
 Example curl request:
 include::{generated}/trace/curl-request.adoc[]
 
-Example HTTP request:
+Example HTTP request: [small]##link:../trace[icon:external-link[role="silver"]]##
 include::{generated}/trace/http-request.adoc[]
 
 Example HTTP response: