Add POST and response.body examples (elastic#13941) (elastic#13952)

* Add  POST and response.body examples

* Moved comments to text

heartbeat/docs/heartbeat-options.asciidoc

@@ -467,11 +467,56 @@ Under `check.request`, specify these options:
 *`headers`*:: A dictionary of additional HTTP headers to send.
 *`body`*:: Optional request body content.
 
+Example configuration:
+This monitor POSTs an `x-www-form-urlencoded` string
+to the endpoint `/demo/add`
+
+[source,yaml]
+-------------------------------------------------------------------------------
+- type: http
+  schedule: '@every 5s'
+  urls: ["http://localhost:8080/demo/add"]
+  check.request:
+    method: POST
+    headers:
+      'Content-Type': 'application/x-www-form-urlencoded'
+    # urlencode the body:
+    body: "name=first&email=someemail%40someemailprovider.com"
+  check.response:
+    status: 200
+    body:
+      - Saved
+      - saved
+-------------------------------------------------------------------------------
+
 Under `check.response`, specify these options:
 
 *`status`*:: The expected status code. 4xx and 5xx codes are considered `down` by default. Other codes are considered `up`.
 *`headers`*:: The required response headers.
 *`body`*:: A list of regular expressions to match the the body output. Only a single expression needs to match.
+
+Example configuration:
+This monitor examines the
+response body for the strings `saved` or `Saved`
+
+[source,yaml]
+-------------------------------------------------------------------------------
+- type: http
+  schedule: '@every 5s'
+  urls: ["http://localhost:8080/demo/add"]
+  check.request:
+    method: POST
+    headers:
+      'Content-Type': 'application/x-www-form-urlencoded'
+    # urlencode the body:
+    body: "name=first&email=someemail%40someemailprovider.com"
+  check.response:
+    status: 200
+    body:
+      - Saved
+      - saved
+-------------------------------------------------------------------------------
+
 *`json`*:: A list of <<conditions,condition>> expressions executed against the body when parsed as JSON.
 
 The following configuration shows how to check the response when the body