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

db/migrate/20220101224048_create_good_jobs.rb

@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+class CreateGoodJobs < ActiveRecord::Migration[6.1]
+  def change
+    enable_extension 'pgcrypto'
+
+    create_table :good_jobs, id: :uuid do |t|
+      t.text :queue_name
+      t.integer :priority
+      t.jsonb :serialized_params
+      t.timestamp :scheduled_at
+      t.timestamp :performed_at
+      t.timestamp :finished_at
+      t.text :error
+
+      t.timestamps
+
+      t.uuid :active_job_id
+      t.text :concurrency_key
+      t.text :cron_key
+      t.uuid :retried_good_job_id
+      t.timestamp :cron_at
+    end
+
+    create_table :good_job_processes, id: :uuid do |t|
+      t.timestamps
+      t.jsonb :state
+    end
+
+    add_index :good_jobs, :scheduled_at, where: "(finished_at IS NULL)", name: "index_good_jobs_on_scheduled_at"
+    add_index :good_jobs, [:queue_name, :scheduled_at], where: "(finished_at IS NULL)", name: :index_good_jobs_on_queue_name_and_scheduled_at
+    add_index :good_jobs, [:active_job_id, :created_at], name: :index_good_jobs_on_active_job_id_and_created_at
+    add_index :good_jobs, :concurrency_key, where: "(finished_at IS NULL)", name: :index_good_jobs_on_concurrency_key_when_unfinished
+    add_index :good_jobs, [:cron_key, :created_at], name: :index_good_jobs_on_cron_key_and_created_at
+    add_index :good_jobs, [:cron_key, :cron_at], name: :index_good_jobs_on_cron_key_and_cron_at, unique: true
+  end
+end