Add Google Analytics

Add Google Analytics tracking

RTPs and Webmasters all have access to Google Analytics, it would be great to add additional sites to those stats so we can see what services are the most used within CSH.

Please ask an RTP or Webmaster for a tracking code and add the tracking to the site.

```

window.dataLayer = window.dataLayer || [];
function gtag(){dataLayer.push(arguments);}
gtag('js', new Date());

gtag('config', 'UA-420696-9');

```

Additionally we can also add a tag to associate sessions with CSH accounts on services that require auth by adding:
```
gtag('set', {'user_id': 'matted'}); // Set the user ID using signed-in user_id
```

No file or test is named. First locate the gallery site's shared page template or entry point, then obtain the tracking code from an RTP or Webmaster and determine whether authenticated services expose the signed-in user ID. Done means Google Analytics tracking is included for the site and, where applicable, sessions are associated with CSH accounts.

Rédigé par le modèle d'indexation à partir du texte de l'issue.