[DOCS] Remove highlights from Installation Guide (#2267)

Co-authored-by: István Zoltán Szabó <istvan.szabo@elastic.co>

Author: lcawl

docs/en/install-upgrade/highlights.asciidoc

@@ -35,8 +35,6 @@ include::upgrading-kibana.asciidoc[]
 
 // include::upgrading-agent.asciidoc[]
 
-include::highlights.asciidoc[]
-
 include::breaking.asciidoc[]
 
 include::redirects.asciidoc[]

docs/en/install-upgrade/index.asciidoc

@@ -13,10 +13,16 @@ This page no longer exists. For the latest breaking changes, refer to
 === APM highlights
 
 This page no longer exists.
-See <<observability-highlights>> for a list of what's new in Elastic Observability.
+See {observability-guide}/whats-new.html[Observability highlights] for a list of what's new in Elastic Observability.
 
 [role="exclude",id="beats-highlights"]
 === Beats highlights
 
 This page no longer exists.
-See <<observability-highlights>> for a list of what's new in Elastic Observability.
+See the {observability-guide}/whats-new.html[Observability highlights] page for a list of what's new in Elastic Observability.
+
+[role="exclude",id="elastic-stack-highlights"]
+=== Highlights
+
+This page no longer exists.
+Go to {estc-welcome}/new.html[Check out the latest from Elastic].