Add GoodJob gem.

This is the first step towards replacing DelayedJob with GoodJob. Compared to
DelayedJob:

* GoodJob supports Rails 7 (DelayedJob is currently a blocker for Rails 7
  because it has a version bound on ActiveRecord <6.2).
* GoodJob has a builtin admin dashboard.
* GoodJob supports threaded job workers.
* GoodJob supports scheduled cronjobs.
* GoodJob supports healthchecks for workers.
* GoodJob uses Postgres notifications instead of polling to pick up new
  jobs. This allows jobs to be picked up faster and scales better with
  large numbers of workers.

https://github.com/bensheldon/good_job

Gemfile

@@ -56,6 +56,7 @@ gem "pry-byebug"
 gem "pry-rails"
 gem "ffi"
 gem "rbtrace"
+gem "good_job"
 
 group :development do
   gem 'rubocop', require: false