adds gtm script (#5597)

Author: Stephen Cefali

gatsby-ssr.js

@@ -23,3 +23,31 @@ export const onPreRenderHTML = ({getHeadComponents}) => {
         }
     })
 };
+
+export const onRenderBody = ({ setHeadComponents }) => {
+    setHeadComponents([
+      // Set up the data layer, enable privacy defaults
+      <script
+        key="gtm-data-layer"
+        type="text/javascript"
+        dangerouslySetInnerHTML={{
+          __html: `
+          (function(w, l) {
+            w[l] = w[l] || [];
+            if(/in-app/.test(window.location.pathname)){
+              w[l].push({ 'disableDrift': 'true' })
+            }
+            w[l].push({ 'gtm.start': new Date().getTime(), event: 'gtm.js' })
+          })(window, 'dataLayer');
+        `,
+        }}
+      />,
+      // Fetch Tag Manager
+      <script
+        key="gtm-script"
+        src={`https://www.googletagmanager.com/gtm.js?id=GTM-N72TJRH`}
+        async={true}
+      />,
+    ]);
+  };
+