add ap-reference folder to floating page exception list

Author: Blargian

plugins/frontmatter-validation/frontmatter-exceptions.txt

@@ -13,4 +13,5 @@
 # /docs\/imports\/.*\.mdx/
 # /\.temp\./
 
-docs/i18n/.*
+docs/i18n/.*
+docs/use-cases/observability/clickstack/api-reference/.*