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/models/captain/assistant_response.rb

@@ -2,22 +2,23 @@
 #
 # Table name: captain_assistant_responses
 #
-#  id           :bigint           not null, primary key
-#  answer       :text             not null
-#  embedding    :vector(1536)
-#  question     :string           not null
-#  status       :integer          default("approved"), not null
-#  created_at   :datetime         not null
-#  updated_at   :datetime         not null
-#  account_id   :bigint           not null
-#  assistant_id :bigint           not null
-#  document_id  :bigint
+#  id                :bigint           not null, primary key
+#  answer            :text             not null
+#  documentable_type :string
+#  embedding         :vector(1536)
+#  question          :string           not null
+#  status            :integer          default("approved"), not null
+#  created_at        :datetime         not null
+#  updated_at        :datetime         not null
+#  account_id        :bigint           not null
+#  assistant_id      :bigint           not null
+#  documentable_id   :bigint
 #
 # Indexes
 #
+#  idx_cap_asst_resp_on_documentable                  (documentable_id,documentable_type)
 #  index_captain_assistant_responses_on_account_id    (account_id)
 #  index_captain_assistant_responses_on_assistant_id  (assistant_id)
-#  index_captain_assistant_responses_on_document_id   (document_id)
 #  index_captain_assistant_responses_on_status        (status)
 #  vector_idx_knowledge_entries_embedding             (embedding) USING ivfflat
 #
@@ -26,7 +27,7 @@ class Captain::AssistantResponse < ApplicationRecord
 
   belongs_to :assistant, class_name: 'Captain::Assistant'
   belongs_to :account
-  belongs_to :document, optional: true, class_name: 'Captain::Document'
+  belongs_to :documentable, polymorphic: true, optional: true
   has_neighbors :embedding, normalize: true
 
   validates :question, presence: true

enterprise/app/models/captain/document.rb

@@ -23,7 +23,7 @@ class Captain::Document < ApplicationRecord
   self.table_name = 'captain_documents'
 
   belongs_to :assistant, class_name: 'Captain::Assistant'
-  has_many :responses, class_name: 'Captain::AssistantResponse', dependent: :destroy
+  has_many :responses, class_name: 'Captain::AssistantResponse', dependent: :destroy, as: :documentable
   belongs_to :account
 
   validates :external_link, presence: true

enterprise/app/models/enterprise/concerns/conversation.rb

@@ -5,6 +5,7 @@ module Enterprise::Concerns::Conversation
     belongs_to :sla_policy, optional: true
     has_one :applied_sla, dependent: :destroy_async
     has_many :sla_events, dependent: :destroy_async
+    has_many :captain_responses, class_name: 'Captain::AssistantResponse', dependent: :nullify, as: :documentable
     before_validation :validate_sla_policy, if: -> { sla_policy_id_changed? }
     around_save :ensure_applied_sla_is_created, if: -> { sla_policy_id_changed? }
   end

enterprise/app/models/enterprise/concerns/user.rb

@@ -3,6 +3,8 @@ module Enterprise::Concerns::User
 
   included do
     before_validation :ensure_installation_pricing_plan_quantity, on: :create
+
+    has_many :captain_responses, class_name: 'Captain::AssistantResponse', dependent: :nullify, as: :documentable
   end
 
   def ensure_installation_pricing_plan_quantity