Replace tutorial modal with welcome e-mail (#6273)

* Remove onboarding modal

* Welcome e-mail

* Send welcome e-mail after confirmation

* Remove obsolete translations

app/mailers/user_mailer.rb

@@ -54,4 +54,15 @@ class UserMailer < Devise::Mailer
       mail to: @resource.email, subject: I18n.t('devise.mailer.email_changed.subject')
     end
   end
+
+  def welcome(user)
+    @resource = user
+    @instance = Rails.configuration.x.local_domain
+
+    return if @resource.disabled?
+
+    I18n.with_locale(@resource.locale || I18n.default_locale) do
+      mail to: @resource.email, subject: I18n.t('user_mailer.welcome.subject')
+    end
+  end
 end