Add new clean GA4 tag (G-4NH21XZLBN) for GitHub Pages

Author: bsayli

docs/_includes/head_custom.html

@@ -1,8 +1,8 @@
 <!-- Google Analytics 4 -->
-<script async src="https://www.googletagmanager.com/gtag/js?id=G-HMPG85XV29"></script>
+<script async src="https://www.googletagmanager.com/gtag/js?id=G-4NH21XZLBN"></script>
 <script>
     window.dataLayer = window.dataLayer || [];
     function gtag(){dataLayer.push(arguments);}
     gtag('js', new Date());
-    gtag('config', 'G-HMPG85XV29');
+    gtag('config', 'G-4NH21XZLBN');
 </script>