Add 'Fetch Event' Admin API page to the docs SUMMARY.md

Otherwise it won't appear on the documentation website's sidebar.

Author: anoadragon453

docs/SUMMARY.md

@@ -60,6 +60,7 @@
     - [Admin API](usage/administration/admin_api/README.md)
       - [Account Validity](admin_api/account_validity.md)
       - [Background Updates](usage/administration/admin_api/background_updates.md)
+      - [Fetch Event](admin_api/fetch_event.md)
       - [Event Reports](admin_api/event_reports.md)
       - [Experimental Features](admin_api/experimental_features.md)
       - [Media](admin_api/media_admin_api.md)