Improve hooks view performance

`.count` always executes an SQL query.
The records need to be loaded anyway
so using `load.size` would save us one query.

app/views/shared/web_hooks/_index.html.haml

@@ -3,7 +3,7 @@
   .card-header
     %h5
       = hook_class.underscore.humanize.titleize.pluralize
-      (#{hooks.count})
+      (#{hooks.load.size})
 
   - if hooks.any?
     %ul.content-list

changelogs/unreleased/improve_webhooks_view_performance.yml

+---
+title: Reduce SQL queries when rendering webhook settings
+merge_request: 27359
+author:
+type: performance