[DOCS] Adds release highlights placeholder

Author: lcawl

docs/reference/release-notes/highlights-7.8.0.asciidoc

@@ -0,0 +1,13 @@
+[[release-highlights-7.8.0]]
+== 7.8.0 release highlights
+++++
+<titleabbrev>7.8.0</titleabbrev>
+++++
+
+coming[7.8.0]
+//NOTE: The notable-highlights tagged regions are re-used in the
+//Installation and Upgrade Guide
+
+// tag::notable-highlights[]
+
+// end::notable-highlights[]

docs/reference/release-notes/highlights.asciidoc

@@ -6,6 +6,7 @@
 This section summarizes the most important changes in each release. For the
 full list, see <<es-release-notes>> and <<breaking-changes>>.
 
+* <<release-highlights-7.8.0>>
 * <<release-highlights-7.7.0>>
 * <<release-highlights-7.6.0>>
 * <<release-highlights-7.5.0>>
@@ -17,6 +18,7 @@ full list, see <<es-release-notes>> and <<breaking-changes>>.
 
 --
 
+include::highlights-7.8.0.asciidoc[]
 include::highlights-7.7.0.asciidoc[]
 include::highlights-7.6.0.asciidoc[]
 include::highlights-7.5.0.asciidoc[]