jobs: switch from DelayedJob to GoodJob.

Switch the ActiveJob backend from DelayedJob to GoodJob. Differences:

* The job worker is run with `bin/good_job start` instead of `bin/delayed_job`.
* Jobs have an 8 hour timeout instead of a 4 hour timeout.
* Jobs don't automatically retry on failure.
* Finishing jobs are preserved and pruned after 7 days.

config/initializers/good_job.rb

@@ -0,0 +1,5 @@
+GoodJob.retry_on_unhandled_error = false
+GoodJob.preserve_job_records = true
+GoodJob.on_thread_error = ->(exception) do
+  DanbooruLogger.log(exception)
+end