DOC-1928: Add 'experimental' attribute to enable UI Macros (see https://docs.antora.org/antora/3.0/asciidoc/ui-macros/#set-the-experimental-attribute)

Author: Farzad Hayatbakhsh

antora.yml

@@ -6,6 +6,7 @@ asciidoc:
     # anchor configuration (the @ allows it to be overridden if required)
     idprefix: '@'
     idseparator: '-@'
+    experimental: ''
     # generic variables
     companyurl: https://www.tiny.cloud
     cdnurl: https://cdn.tiny.cloud/1/no-api-key/tinymce/7/tinymce.min.js