update mkdocs, event handler menu

Author: hjgraca

mkdocs.yml

@@ -21,7 +21,8 @@ nav:
           - core/metrics.md
           - core/metrics-v2.md
       - core/tracing.md
-      - core/event_handler/appsync_events.md
+      - Event Handler:
+          - core/event_handler/appsync_events.md
   - Utilities:
       - utilities/parameters.md
       - utilities/idempotency.md