Add GoogleTagManager to Docs Site

Marketing has asked that we implement GTM so they can better understand how outside people are using Cauldron, we would need to include the following script:

```js

(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-T2FM2TZ7');

```

Since Cauldron doesn't currently implement any kind of tracking behaviors, we need to determine if there are any additional things that we would need to include to gain consent (such as a cookie consent banner).

Start by locating the Docs Site entry point and checking how site-wide scripts and any consent or privacy behavior are configured. Confirm the Google Tag Manager requirement and determine whether consent handling is needed; done means the agreed tracking and consent behavior is documented and implemented for the Docs Site.

Written by the indexing model from the issue text.