chore: add google-analytics.html

Author: netomi

_includes/google-analytics.html

@@ -0,0 +1,8 @@
+<!-- Global site tag (gtag.js) - Google Analytics -->
+<script async src="https://www.googletagmanager.com/gtag/js?id={{ site.google_analytics }}"></script>
+<script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+    gtag('config', '{{ site.google_analytics }}');
+</script>