[DR-371] Added meta pixel to docs pages (#48)

https://reddit.atlassian.net/browse/DR-371

<!-- If this pull request closes an issue, please mention the issue
number below -->
Closes # <!-- Issue # here -->

## 💸 TL;DR
<!-- What's the three sentence summary of purpose of the PR -->

## 📜 Details
[Design Doc](<!-- insert Google Doc link here if applicable -->)

[Jira](<!-- insert Jira link if applicable -->)

<!-- Add additional details required for the PR: breaking changes,
screenshots, external dependency changes -->

## 🧪 Testing Steps / Validation
<!-- add details on how this PR has been tested, include reproductions
and screenshots where applicable -->

## ✅ Checks
<!-- Make sure your pr passes the CI checks and do check the following
fields as needed - -->
- [ ] CI tests (if present) are passing
- [ ] Adheres to code style for repo
- [ ] Contributor License Agreement (CLA) completed if not a Reddit
employee

Author: RedditParadox

docusaurus.config.ts

@@ -23,6 +23,25 @@ const config: Config = {
       onBrokenMarkdownLinks: "throw",
     },
   },
+  headTags: [
+    // Added to headTags instead of scripts to keep the script and noscript tags together
+    // Start meta tag for Facebook Pixel DR-371
+    {
+      tagName: "script",
+      attributes: {},
+      innerHTML: `!function(f,b,e,v,n,t,s)
+              {if(f.fbq)return;n=f.fbq=function(){n.callMethod?
+              n.callMethod.apply(n,arguments):n.queue.push(arguments)};
+              if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';
+              n.queue=[];t=b.createElement(e);t.async=!0;
+              t.src=v;s=b.getElementsByTagName(e)[0];
+              s.parentNode.insertBefore(t,s)}(window, document,'script',
+              'https://connect.facebook.net/en_US/fbevents.js');
+              fbq('init', '4294970040755652');
+              fbq('track', 'PageView');`,
+    },
+    // End meta tag for Facebook Pixel
+  ],
   scripts: [
     {
       src: "https://widget.kapa.ai/kapa-widget.bundle.js",