Fix parent_document_url not being sent to asset manager for consultation outcome attachments

When a consultation is published, PublishAttachmentAssetJob updates each
attachment's metadata in asset manager. For attachments belonging to a
Consultation Outcome, `parent_document_url` was never sent because the job guards with `respond_to?(:public_url)` and Consultation Response did not implement that method.

I've extended ConsultationResponse, so the parent consultation's public URL is used as `parent_document_url`.

Known limitation: `attachable_url` in AttachmentData is used by
`AssetManagerAttachmentMetadataJob` when an attachment is saved or updated on a draft consultation. The `parent_document_url` sent to asset manager will still be `nil` in such case. This is because `visible_edition_for` filters to Edition subclasses only, and
ConsultationResponse is not an Edition.

In essence, `parent_document_url` is only reliably set at document publish time.
Extending `attachable_url` to handle non-edition attachables with a public URL would be great as a follow-up work.

Author: eYinka

app/models/consultation_response.rb

@@ -33,6 +33,8 @@ def access_limited_object
 
   delegate :unpublishing, to: :parent_attachable
 
+  delegate :public_url, to: :parent_attachable
+
   def can_order_attachments?
     true
   end

test/unit/app/sidekiq/publish_attachment_asset_job_test.rb

@@ -59,5 +59,26 @@ class PublishAttachmentAssetJobTest < ActiveSupport::TestCase
         job.perform(attachment_data.id)
       end
     end
+
+    context "attachment belongs to a consultation outcome" do
+      let(:consultation) { create(:published_consultation, title: "my-consultation") }
+      let(:outcome) { create(:consultation_outcome, consultation:) }
+      let(:attachment_data) { create(:attachment_data, attachable: outcome) }
+      let(:attachment) { create(:file_attachment, attachable: outcome, attachment_data:) }
+
+      before do
+        attachment_data.attachments = [attachment]
+        attachment_data.save!
+      end
+
+      it "updates the asset with the parent consultation's public URL" do
+        AssetManager::AssetUpdater.expects(:call).with(
+          asset_manager_id,
+          { "draft" => false, "parent_document_url" => "https://www.test.gov.uk/government/consultations/my-consultation" },
+        )
+
+        job.perform(attachment_data.id)
+      end
+    end
   end
 end