Add conditional tracking pixel (#126)

Author: eric-schneider

src/partials/body-end-scripts.hbs

@@ -2,7 +2,6 @@
 <script data-sync-storage-key="preferred-tab" async src="{{{uiRootPath}}}/js/vendor/tabs.js"></script>
 <script async src="{{{uiRootPath}}}/js/vendor/highlight.js"></script>
 <script async src="{{{uiRootPath}}}/js/vendor/zooming.js"></script>
-
 <script src="https://cdn.jsdelivr.net/npm/@docsearch/js@3"></script>
 {{#with site.keys}}
   {{#if (and algoliaAppId algoliaIndexName algoliaApiKey)}}
@@ -18,3 +17,4 @@
   {{/if}}
 {{/with}}
 {{> intercom}}
+{{> scarf}}

src/partials/scarf.hbs

@@ -0,0 +1,4 @@
+{{#with site.keys.scarfTrackingPixel}}
+<img referrerpolicy="no-referrer-when-downgrade" src="https://static.scarf.sh/a.png?x-pxid={{this}}"
+  style="display:none" />
+{{/with}}