[Internal] Add experimental tag

Author: avijeet95

.codegen/changelog_config.yml

@@ -7,6 +7,8 @@ change_types:
     tag: "[Doc]"
   - message: Internal Changes
     tag: "[Internal]"
+  - message: Experimental Changes
+    tag: "[Experimental]"
   # Does not appear in the Changelog. Only for PR validation.
   - message: Release
     tag: "[Release]"