finished_at should be indexed and clean up should clean up all of a job's executions

[zarqman]

Thanks for adding the new option to automatically cleanup preserved jobs!

I noticed that GoodJob::Execution.finished(timestamp).delete_all inside of cleanup_preserved_jobs is querying finished_at but that column isn't indexed resulting in a table scan. I'm thinking finished_at needs an index (possibly conditional on being not null)?

[bensheldon]

@zarqman thank you! 🙏

I'll add an index. That also caused me to notice that the cleanup task should retain Execution records until the Job itself completes successfully, then cleanup all the Job's executions at once.