added the Beam 3.0.0 highlights to the release template (#34556)

Author: liferoad

CHANGES.md

@@ -20,6 +20,10 @@
 <!--
 # [2.XX.X] - Unreleased
 
+## Beam 3.0.0 Development Highlights
+
+* New highly anticipated feature ([X](https://github.com/apache/beam/issues/X)) to address Milestone Y ([#Y](https://github.com/apache/beam/issues/Y)).
+
 ## Highlights
 
 * New highly anticipated feature X added to Python SDK ([#X](https://github.com/apache/beam/issues/X)).