Merge branch 'add-smtp-setting' into 'master'

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

Something happened after upgrading to 8.9RC5 that caused mail settings to be set to sendmail by default. gitlab-com/infrastructure#128 describes the issue in more detail. This MR mirrors the change in omnibus with gitlab-org/omnibus-gitlab!826.

Closes #19132

See merge request !4915

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,