Revert "Remove conversation URI (#11423)" (#11424)

This reverts commit 75f7f9930e.

spec/models/conversation_spec.rb

@@ -1,5 +1,13 @@
 require 'rails_helper'
 
 RSpec.describe Conversation, type: :model do
+  describe '#local?' do
+    it 'returns true when URI is nil' do
+      expect(Fabricate(:conversation).local?).to be true
+    end
 
+    it 'returns false when URI is not nil' do
+      expect(Fabricate(:conversation, uri: 'abc').local?).to be false
+    end
+  end
 end