Enable action_mailer in a minimal railsapp.

2021-05-04 rails

Once you've created rails project with --minimal option, you'll see the following settings in config/application.rb

# Pick the frameworks you want:
require "active_model/railtie"
# require "active_job/railtie"
require "active_record/railtie"
# require "active_storage/engine"
require "action_controller/railtie"
# require "action_mailer/railtie"
# require "action_mailbox/engine"
# require "action_text/engine"
require "action_view/railtie"
# require "action_cable/engine"
require "sprockets/railtie"
require "rails/test_unit/railtie"