Add (optional) Sentry integration

A Sentry DSN can be set via `SENTRY_DSN` and authenticated users will be
tagged with ID and username (cn) in events.

config/initializers/sentry.rb

@@ -0,0 +1,9 @@
+if ENV["SENTRY_DSN"].present?
+  Sentry.init do |config|
+    config.dsn = ENV["SENTRY_DSN"]
+    config.breadcrumbs_logger = [:active_support_logger, :http_logger]
+    config.traces_sampler = lambda do |context|
+      true
+    end
+  end
+end

config/routes.rb

@@ -1,7 +1,7 @@
 require 'sidekiq/web'
 
 Rails.application.routes.draw do
-  devise_for :users, :controllers => { :confirmations => "users/confirmations" }
+  devise_for :users, controllers: { confirmations: "users/confirmations" }
 
   get 'welcome', to: 'welcome#index'
   get 'check_your_email', to: 'welcome#check_your_email'