Add release note for function alias

Change-Id: I9dc8ecd6cbf87b44e84263615ea38582dfbf8aa2
Story: 2002143
Task: 22518

releasenotes/notes/function-aliasing-318abd48128b4084.yaml

@@ -0,0 +1,5 @@
+---
+features:
+  - Support alias for functions. Users can create function alias
+    pointing to the specific function version. Function alias can be used
+    for creating execution, job and webhook.