added beta tag to sites (#19907)

Author: marciocloudflare

src/content/docs/magic-wan/configuration/common-settings/sites.mdx

@@ -3,6 +3,8 @@ title: Set up a site
 pcx_content_type: how-to
 sidebar:
   order: 2
+  badge:
+    text: Beta
 ---
 
 import { Details } from "~/components"