GA: Add Google Analytics snippets

Signed-off-by: Youngsoo Shin <sysx114@gmail.com>

Writerside/cfg/google.head.html

@@ -0,0 +1,9 @@
+<!-- Google tag (gtag.js) -->
+<script async src="https://www.googletagmanager.com/gtag/js?id=G-8BTPRBKJ5B"></script>
+<script>
+    window.dataLayer = window.dataLayer || [];
+    function gtag(){dataLayer.push(arguments);}
+    gtag('js', new Date());
+
+    gtag('config', 'G-8BTPRBKJ5B');
+</script>