Register all action mailer interceptors in a single place

config/initializers/disable_email_interceptor.rb → config/initializers/action_mailer_hooks.rb

@@ -2,3 +2,6 @@ unless Gitlab.config.gitlab.email_enabled
   ActionMailer::Base.register_interceptor(::Gitlab::Email::Hook::DisableEmailInterceptor)
   ActionMailer::Base.logger = nil
 end
+
+ActionMailer::Base.register_interceptor(::Gitlab::Email::Hook::AdditionalHeadersInterceptor)
+ActionMailer::Base.register_interceptor(::Gitlab::Email::Hook::EmailTemplateInterceptor)

config/initializers/additional_headers_interceptor.rb

-ActionMailer::Base
-  .register_interceptor(::Gitlab::Email::Hook::AdditionalHeadersInterceptor)

config/initializers/email_template_interceptor.rb

-ActionMailer::Base.register_interceptor(::Gitlab::Email::Hook::EmailTemplateInterceptor)