DEV: Require pry-byebug in development mode (#18952)

We already do this in test mode, so let's do it in
development mode too. It adds better step-by-step
debugging and callstack navigation, see the readme
for more details:

https://github.com/deivid-rodriguez/pry-byebug

config/application.rb

@@ -58,6 +58,7 @@ if !GlobalSetting.skip_redis?
 end
 
 require 'pry-rails' if Rails.env.development?
+require 'pry-byebug' if Rails.env.development?
 
 require 'discourse_fonts'