Add new marketing callout content and unhide (#2857)

* Add new marketing callout content and unhide

* Add cache buster to force reloading of JavaScript

extra/docs_landing.html

@@ -304,7 +304,6 @@
     padding: 80px 0 96px;
     margin: 96px 0;
     position: relative;
-    display: none;
   }
 
   #guide .marketing-callout h2 {
@@ -687,11 +686,10 @@ <h3 class="mt-3">
 
 <div id="bottomContent" style="display: none;">
   <div class="marketing-callout">
-    <h2>Elastic ON Tour registration is live!</h2>
-    <p>Join us for a day full of Elastic learning and networking. Find an ElasticON event near you.</p>
+    <h2>Free Elastic training</h2>
+    <p>Learn about Elasticsearch Relevance Engine™ (ESRE), designed to power AI search applications.</p>
     <a class="button btn-primary btn-small"
-      href="https://www.elastic.co/events/elasticon?utm_campaign=elasticon-tour-overview&utm_source=website&utm_medium=docs-sidebar">Learn
-      more</a>
+      href="https://www.elastic.co/training/elasticsearch-relevance-engine-quick-start?tech=rtp&plcmt=cta-card&pg=docs">Explore now</a>
   </div>
 
   <div class="my-4 need-help">