chore: Update LLM formatter classes to include additional details (#11491)

This PR introduces support for optionally exposing more data during LLM
function calls. This will be useful as we expand Copilot’s capabilities.

Changes included:
- Add support for ArticleLlmFormatter
- Add missing specs for ContactLLMFormatter and ArticleLLMFormatter
- Add additional spec for ConversationLLMFormatter based on config

app/models/article.rb

@@ -33,6 +33,7 @@
 #
 class Article < ApplicationRecord
   include PgSearch::Model
+  include LlmFormattable
 
   has_many :associated_articles,
            class_name: :Article,