feat: Add a sort option for conversations waiting for a reply from an agent (#7364)

spec/presenters/conversations/event_data_presenter_spec.rb

@@ -31,6 +31,7 @@ RSpec.describe Conversations::EventDataPresenter do
         contact_last_seen_at: conversation.contact_last_seen_at.to_i,
         agent_last_seen_at: conversation.agent_last_seen_at.to_i,
         created_at: conversation.created_at.to_i,
+        waiting_since: conversation.waiting_since.to_i,
         priority: nil,
         unread_count: 0
       }