Renamed internal docs id for the extension guide

Author: dgomezg

docs/_playbook/playbook.yaml

@@ -1,6 +1,6 @@
 site:
   title: Kotlin Extension docs PREVIEW
-  start_page: kotlin_extension_old_ref::index.adoc
+  start_page: kotlin_extension_guide::index.adoc
 
 content:
   sources:

docs/old-reference-guide/antora.yml

@@ -1,12 +1,12 @@
-name: kotlin_extension_old_ref
+name: kotlin_extension_guide
 title: Kotlin Extension Guide
 version: true
 prerelease: true
 start_page: ROOT:index.adoc
 
 asciidoc:
   attributes:
-    component_description: The Kotlin xtension guide from the former reference guide
+    component_description: The Kotlin Extension Guide from the former reference guide
     type: guide
     group: axon-framework