[DOCS] Adds link to 6.3.0 release highlights

Author: lcawl

docs/reference/release-notes/highlights-6.4.0.asciidoc

@@ -4,8 +4,6 @@
 <titleabbrev>6.4.0</titleabbrev>
 ++++
 
-coming[6.4.0]
-
 See also <<release-notes-6.4.0,{es} 6.4.0 release notes>>. 
 
 [float]

docs/reference/release-notes/highlights-6.5.0.asciidoc

@@ -0,0 +1,7 @@
+[[release-highlights-6.5.0]]
+== 6.5.0 release highlights
+++++
+<titleabbrev>6.5.0</titleabbrev>
+++++
+
+coming[6.5.0]

docs/reference/release-notes/highlights.asciidoc

@@ -10,7 +10,9 @@ This section summarizes the most important changes in each release. For the
 full list, see <<es-release-notes>> and <<breaking-changes>>. 
 
 * <<release-highlights-6.4.0>>
+* <<release-highlights-6.3.0>>
 
 --
 
-include::highlights-6.4.0.asciidoc[]
+include::highlights-6.4.0.asciidoc[]
+include::highlights-6.3.0.asciidoc[]