Add google tag manager script (#697)

Author: toppare

docusaurus.config.js

@@ -62,6 +62,9 @@ const config = {
         theme: {
           customCss: "./src/css/custom.css",
         },
+        googleTagManager: {
+          containerId: 'GTM-NJWQK6DX',
+        },
       }),
     ],
     [