Add healthcheck endpoint. (#254)

Author: conradwt

config/routes.rb

@@ -1,6 +1,8 @@
 # frozen_string_literal: true
 
 Rails.application.routes.draw do
+  get "/healthz" => "rails/health#show", as: :rails_health_check
+
   if Rails.env.development? or Rails.env.test?
     mount GraphiQL::Rails::Engine, at: '/graphiql', graphql_path: '/graphql'
   end