feat: add google tag manager

layouts/partials/footer/custom.html

@@ -0,0 +1,4 @@
+<!-- Google Tag Manager (noscript) -->
+<noscript><iframe src="https://www.googletagmanager.com/ns.html?id=GTM-MCTV2KJL"
+  height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript>
+  <!-- End Google Tag Manager (noscript) -->

layouts/partials/head/custom.html

@@ -0,0 +1,7 @@
+<!-- Google Tag Manager -->
+<script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':
+  new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],
+  j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src=
+  'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);
+  })(window,document,'script','dataLayer','GTM-MCTV2KJL');</script>
+  <!-- End Google Tag Manager -->