JENKINS-20780 Wrap timezone list in collapsible details section

Author: AmoghParmar

core/src/main/resources/hudson/triggers/TimerTrigger/help-spec.jelly

@@ -91,26 +91,27 @@ H H 1,15 1-11 *
   first line of the field.
   Time zone specification starts with <code>TZ=</code>, followed by the ID of a time zone.
 </p>
+  <p>
+    Complete example of a schedule with a time zone specification:
+  </p>
+  <pre>
+    TZ=Europe/London
+    # This job needs to be run in the morning, London time
+    H 8 * * *
+    # Butlers do not have a five o'clock, so we run the job again
+    H(0-30) 17 * * *
+  </pre>
 <p>
-  Complete example of a schedule with a time zone specification:
-</p>
-<pre>
-  TZ=Europe/London
-  # This job needs to be run in the morning, London time
-  H 8 * * *
-  # Butlers do not have a five o'clock, so we run the job again
-  H(0-30) 17 * * *
-</pre>
-<p>
-  The full list of supported time zone IDs depends on the Java runtime Jenkins is running on.
-  A reference list of TZ database time zone IDs can be found here:
-  <a href="https://en.wikipedia.org/wiki/List_of_tz_database_time_zones" target="_blank">
-    List of tz database time zones
-  </a>.
-</p>
-<p>
-  Most users will not need to set a custom time zone. Only specify one if your job must run
-  in a different time zone than the Jenkins controller.
+  The supported time zones depend on the Java runtime Jenkins is running on. The list of supported time zone IDs on this instance is:
 </p>
+<details>
+  <summary><strong>Click to view the list of supported time zone IDs</strong></summary>
+  <j:invokeStatic className="java.util.TimeZone" method="getAvailableIDs" var="timeZones"/>
+  <ul>
+    <j:forEach items="${timeZones}" var="timeZone">
+      <li>${timeZone}</li>
+    </j:forEach>
+  </ul>
+</details>
 </div>
 </j:jelly>