Restart DelayedJob workers after they crash

DelayedJob offers the `--monitor` (aliased as `-m`) option to create a
process that monitors the workers and restarts them when they crash.

This change implies that, in order to stop the delayed job workers, we
now need to pass the `-n` option when running `bin/delayed_job stop`:
`RAILS_ENV=production bin/delayed_job -n 2 stop`.

config/deploy.rb

@@ -40,6 +40,7 @@ set :puma_conf, "#{release_path}/config/puma/#{fetch(:rails_env)}.rb"
 
 set :delayed_job_workers, 2
 set :delayed_job_roles, :background
+set :delayed_job_monitor, true
 
 set :whenever_roles, -> { :app }
 

config/schedule.rb

@@ -42,5 +42,5 @@ end
 every :reboot do
   command "cd #{@path} && bundle exec puma -C config/puma/#{@environment}.rb"
   # Number of workers must be kept in sync with capistrano's delayed_job_workers
-  command "cd #{@path} && RAILS_ENV=#{@environment} bin/delayed_job -n 2 restart"
+  command "cd #{@path} && RAILS_ENV=#{@environment} bin/delayed_job -m -n 2 restart"
 end