Add Plausible to Nebula docs (#289)

Add Plausible to Nebula docs to test out how it works across multiple
subdomains.

Verified it works on the preview URL:
<img width="1116" height="613" alt="image"
src="https://github.com/user-attachments/assets/8e477a37-acb0-47f2-bb19-073706ac02e1"
/>

Author: bgolat

docusaurus.config.cjs

@@ -44,6 +44,14 @@ const config = {
     ],
   ],
 
+  scripts: [
+    {
+      src: 'https://plausible.io/js/pa--fa02jhZoajfPxSb4zpFj.js',
+      async: true,
+    },
+    '/scripts/plausible.js',
+  ],
+
   // Even if you don't use internalization, you can use this field to set useful
   // metadata like html lang. For example, if your site is Chinese, you may want
   // to replace "en" with "zh-Hans".

static/scripts/plausible.js

@@ -0,0 +1,13 @@
+window.plausible =
+  window.plausible ||
+  function () {
+    (window.plausible.q = window.plausible.q || []).push(arguments);
+  };
+
+window.plausible.init =
+  window.plausible.init ||
+  function (options) {
+    window.plausible.o = options || {};
+  };
+
+window.plausible.init();