Create rake task to migrate Setting key from per_page_code to per_page_code_head
user
```ruby
namespace :settings do

  desc "Changes Setting key per_page_code for per_page_code_head"
  task per_page_code_migration: :environment do
    per_page_code_setting = Setting.where(key: 'per_page_code').first

    Setting['per_page_code_head'] = per_page_code_setting&.value.to_s if Setting.where(key: 'per_page_code_head').first.blank?
    per_page_code_setting.destroy if per_page_code_setting.present?
  end

end
```
assistant