feat: Add support for the references in FAQs (#10699)

Currently, it’s unclear whether an FAQ item is generated from a
document, derived from a conversation, or added manually.

This PR resolves the issue by providing visibility into the source of
each FAQ. Users can now see whether an FAQ was generated or manually
added and, if applicable, by whom.

- Move the document_id to a polymorphic relation (documentable).
- Updated the APIs to accommodate the change.
- Update the service to add corresponding references. 
- Updated the specs.

<img width="1007" alt="Screenshot 2025-01-15 at 11 27 56 PM"
src="https://github.com/user-attachments/assets/7d58f798-19c0-4407-b3e2-748a919d14af"
/>

---------

Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

enterprise/app/services/captain/llm/conversation_faq_service.rb

@@ -4,6 +4,7 @@ class Captain::Llm::ConversationFaqService < Captain::Llm::BaseOpenAiService
   def initialize(assistant, conversation, model = DEFAULT_MODEL)
     super()
     @assistant = assistant
+    @conversation = conversation
     @content = conversation.to_llm_text
     @model = model
   end
@@ -19,7 +20,7 @@ class Captain::Llm::ConversationFaqService < Captain::Llm::BaseOpenAiService
 
   private
 
-  attr_reader :content
+  attr_reader :content, :conversation, :assistant
 
   def find_and_separate_duplicates(faqs)
     duplicate_faqs = []
@@ -41,7 +42,7 @@ class Captain::Llm::ConversationFaqService < Captain::Llm::BaseOpenAiService
   end
 
   def find_similar_faqs(embedding)
-    similar_faqs = @assistant
+    similar_faqs = assistant
                    .responses
                    .nearest_neighbors(:embedding, embedding, distance: 'cosine')
     Rails.logger.debug(similar_faqs.map { |faq| [faq.question, faq.neighbor_distance] })
@@ -50,7 +51,12 @@ class Captain::Llm::ConversationFaqService < Captain::Llm::BaseOpenAiService
 
   def save_new_faqs(faqs)
     faqs.map do |faq|
-      @assistant.responses.create!(question: faq['question'], answer: faq['answer'], status: 'pending')
+      assistant.responses.create!(
+        question: faq['question'],
+        answer: faq['answer'],
+        status: 'pending',
+        documentable: conversation
+      )
     end
   end