add stats extension to staging

Author: osfameron

antora-playbook-staging.diff.yml

@@ -1,6 +1,8 @@
 antora:
   extensions:
   - ./lib/report-tree.js
+  - ./lib/site-stats-extension.js
+  - ./lib/component-stats.js
 
 site:
   title: Couchbase Docs Staging

antora-playbook-staging.yml

@@ -26,6 +26,8 @@ antora:
     - ./lib/embargo.js
     - ./lib/antora-component-version-rank.js
     - ./lib/report-tree.js
+    - ./lib/site-stats-extension.js
+    - ./lib/component-stats.js
 site:
   title: Couchbase Docs Staging
   url: https://docs-staging.couchbase.com