Heartbeat: add journey.duration mapping to synthetics event

CHANGELOG.next.asciidoc

@@ -319,6 +319,7 @@ https://github.com/elastic/beats/compare/v8.8.1\...main[Check the HEAD diff]
 
 - Added status to monitor run log report.
 - Upgrade node to latest LTS v18.20.3. {pull}40038[40038]
+- Add journey duration to synthetics browser events. {pull}40230[40230]
 
 *Metricbeat*
 

heartbeat/_meta/fields.common.yml

@@ -248,8 +248,7 @@
         - name: index
           type: integer
           description: >
-            Indexed used for creating total order of all events
-            in this invocation.
+            Index count used for creating total order of all events during invocation.
         - name: payload
           type: object
           enabled: false
@@ -288,6 +287,13 @@
             - name: tags
               description: Tags used for grouping journeys
               type: keyword
+            - name: duration
+              type: group
+              description: Duration required to complete the journey.
+              fields:
+                - name: us
+                  type: integer
+                  description: Duration in microseconds
         - name: error
           type: group
           fields:

heartbeat/docs/fields.asciidoc

@@ -16507,7 +16507,7 @@ type: keyword
 *`synthetics.index`*::
 +
 --
-Indexed used for creating total order of all events in this invocation.
+Index count used for creating total order of all events during invocation.
 
 
 type: integer
@@ -16609,6 +16609,21 @@ type: keyword
 
 --
 
+[float]
+=== duration
+
+Duration required to complete the journey.
+
+
+*`synthetics.journey.duration.us`*::
++
+--
+Duration in microseconds
+
+type: integer
+
+--
+
 
 *`synthetics.error.name`*::
 +