Cherry-pick to 7.9: [docs] Rename release highlights to what's new (elastic#20255) (elastic#20285)

* [docs] Rename release highlights to what's new (elastic#20255)

* Fix versions in placeholder text

Author: dedemorton

libbeat/docs/index.asciidoc

@@ -20,6 +20,8 @@ include::{libbeat-dir}/shared-beats-attributes.asciidoc[]
 
 include::./overview.asciidoc[]
 
+include::./release-notes/whats-new.asciidoc[]
+
 include::./communitybeats.asciidoc[]
 
 include::./getting-started.asciidoc[]
@@ -28,8 +30,6 @@ include::./config-file-format.asciidoc[]
 
 include::./upgrading.asciidoc[]
 
-include::./release-notes/highlights/highlights.asciidoc[]
-
 include::./release-notes/breaking/breaking.asciidoc[]
 
 include::./release.asciidoc[]

libbeat/docs/overview.asciidoc

@@ -1,5 +1,5 @@
 [[beats-reference]]
-== Beats overview
+== What are {beats}?
 
 {beats} are open source data shippers that you install as agents on your
 servers to send operational data to