jobs: add ability to search jobs on /jobs page.

Add ability to search jobs on the /jobs page by job type or by status.

Fixes #2577 (Search filters for delayed jobs). This wasn't possible
before with DelayedJobs because it stored the job data in a YAML string,
which made it difficult to search jobs by type. GoodJobs stores job data
in a JSON object, which is easier to search in Postgres.

app/policies/background_job_policy.rb

@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-class GoodJobPolicy < ApplicationPolicy
+class BackgroundJobPolicy < ApplicationPolicy
   def index?
     true
   end