Add SMTP as default delivery method to match gitlab-org/omnibus-gitlab!826

Closes #19132

[ci skip]

config/initializers/smtp_settings.rb.sample

@@ -10,6 +10,7 @@
 if Rails.env.production?
   Rails.application.config.action_mailer.delivery_method = :smtp
 
+  ActionMailer::Base.delivery_method = :smtp
   ActionMailer::Base.smtp_settings = {
     address: "email.server.com",
     port: 465,