Add /extension path for extension installation (#3011)

documentation/src/pages/extension.tsx

@@ -0,0 +1,17 @@
+import React, { useEffect } from 'react';
+import { useLocation } from '@docusaurus/router';
+
+export default function ExtensionRedirect(): JSX.Element {
+  const location = useLocation();
+
+  useEffect(() => {
+    const params = new URLSearchParams(location.search);
+    window.location.href = `goose://extension${params.toString() ? '?' + params.toString() : ''}`;
+  }, [location]);
+
+  return (
+    <div style={{ padding: '2rem', textAlign: 'center' }}>
+      Redirecting to Goose...
+    </div>
+  );
+}