Add unsubscribe link to e-mails (#25378)

config/routes.rb

@@ -67,6 +67,8 @@ Rails.application.routes.draw do
   devise_scope :user do
     get '/invite/:invite_code', to: 'auth/registrations#new', as: :public_invite
 
+    resource :unsubscribe, only: [:show, :create], controller: :mail_subscriptions
+
     namespace :auth do
       resource :setup, only: [:show, :update], controller: :setup
       resource :challenge, only: [:create], controller: :challenges