Fix stoplight logging to stderr separate from Rails logger (#10624)

config/initializers/stoplight.rb

@@ -1,3 +1,4 @@
 require 'stoplight'
 
 Stoplight::Light.default_data_store = Stoplight::DataStore::Redis.new(Redis.current)
+Stoplight::Light.default_notifiers  = [Stoplight::Notifier::Logger.new(Rails.logger)]