Preserve GoodJob::Jobs when a StandardError is raised

[bensheldon]

As uncovered in #59:

• To be maximally safe by default, if someone has not configured ActiveJob correctly, jobs should be preserved if a StandardError bubbles up from GoodJob::Job#perform
• ActionMailer::DeliveryJob does not inherit from ApplicationJob and is not covered by the documentation's advice to use retry_on

When a ~StandardError bubbles all the way up to the GoodJob adapter, the job will be discarded (marked as finished, or destroyed) the job will be preserved and re-run, unless GoodJob.standard_error_results_in_finished_job (maybe with more words-mithing 😅 ).

Your issue also triggered some more research and it seems that currently ActionMailer::MailDeliveryJob which is used when calling deliver_later on a Mailer) inherits from ActiveJob::Base which means that mailer errors may be incorrectly marked as finished/discarded.