[Fundamentals] Update add-multiple-sites-automation.mdx

Replacing obsolete link.

Author: nenizera

src/content/docs/fundamentals/setup/manage-domains/add-multiple-sites-automation.mdx

@@ -1,6 +1,6 @@
 ---
 pcx_content_type: tutorial
-source: https://support.cloudflare.com/hc/articles/360000841472
+source: https://developers.cloudflare.com/fundamentals/setup/manage-domains/add-multiple-sites-automation/
 title: Add multiple sites via automation
 ---