feat: Add 'html_extension_style: indexify' to playbook

Author: Techassi

antora-playbook.yml

@@ -19,6 +19,8 @@ urls:
   # latest version is not latest anymore, the redirect is instead the actual URL.
   latest_version_segment: stable
   latest_version_segment_strategy: redirect:to
+  # See https://docs.antora.org/antora/latest/playbook/urls-html-extension-style/#html-extension-style-key
+  html_extension_style: indexify
 content:
   sources:
     - url: .