Document HTTP response format of health endpoint

Add HTTP response format details for health endpoint, including default
status codes and sample responses.

See gh-8703

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

@@ -677,9 +677,8 @@ If you don't want to expose endpoints over HTTP you can set the management port
 ----
 
 
-
 [[production-ready-health-access-restrictions]]
-=== HTTP health endpoint access restrictions
+=== HTTP health endpoint format and access restrictions
 The information exposed by the health endpoint varies depending on whether or not it's
 accessed anonymously, and whether or not the enclosing application is secure.
 By default, when accessed anonymously in a secure application, any details about the
@@ -689,6 +688,62 @@ endpoint being used in a denial of service attack. The `endpoints.health.time-to
 property is used to configure the caching period in milliseconds. It defaults to 1000,
 i.e. one second.
 
+The HTTP status code in the response reflects the overall health status (e.g. “UP”=200, 
+“OUT_OF_SERVICE”=503, “DOWN”=503). The mappings can be changed by configuring 
+`endpoints.health.mapping.<STATUS>=XXX`.
+
+Sample summarized HTTP response (default for anonymous request):
+
+[source,indent=0]
+----
+$ curl -i localhost:8080/health
+HTTP/1.1 200
+X-Application-Context: application
+Content-Type: application/vnd.spring-boot.actuator.v1+json;charset=UTF-8
+Content-Length: 15
+
+{"status":"UP"}
+----
+
+Sample summarized HTTP response for status "DOWN" (notice the 503 status code):
+
+[source,indent=0]
+----
+$ curl -i localhost:8080/health
+HTTP/1.1 503
+X-Application-Context: application
+Content-Type: application/vnd.spring-boot.actuator.v1+json;charset=UTF-8
+Content-Length: 17
+
+{"status":"DOWN"}
+----
+
+Sample detailed  HTTP response:
+
+[source,indent=0]
+----
+$ curl -i localhost:8080/health
+HTTP/1.1 200 OK
+X-Application-Context: application
+Content-Type: application/vnd.spring-boot.actuator.v1+json;charset=UTF-8
+Content-Length: 221
+
+{
+  "status" : "UP",
+  "diskSpace" : {
+    "status" : "UP",
+    "total" : 63251804160,
+    "free" : 31316164608,
+    "threshold" : 10485760
+  },
+  "db" : {
+    "status" : "UP",
+    "database" : "H2",
+    "hello" : 1
+  }
+}
+----
+
 The above-described restrictions can be enhanced, thereby allowing only authenticated
 users full access to the health endpoint in a secure application. To do so, set
 `endpoints.health.sensitive` to `true`. Here's a summary of behavior (with default