Recreate cron indexes to be conditional

[defkode]

fixes #1161

[bensheldon]

@defkode sorry, I realized I have so much experience doing this :D

• I think this can be a single migration.
• Indexes are a little weird to do idempotently because each call needs to be wrapped with an if index_exists? check because the migration could fail out somewhere in the middle because of the disable_ddl! removing the transaction wrapper.
• You'll also need to update the templates/install migration
• Then you'll need to run the template generator on the demo app to generate the live database migration files. Then run those which will update the demo app's schema.rb

...so ultimately this should be updates to 4 files:

• lib/generators/good_job/templates/update/migrations/06_recreate_good_job_cron_indexes.rb
• lib/generators/good_job/templates/install/migrations/06_recreate_good_job_cron_indexes.rb
• demo/db/migrate/xxxxx_recreate_good_job_cron_indexes.rb
• demo/db/schema.rb

[defkode]

@bensheldon Thanks for hints. PR is updated.

[bensheldon]

@defkode thank you! I just made a few tweaks. I'm going to let CI run through 💚 and then it should be done ⭐

[bensheldon]

I'm pretty certain this is failing because of a change introduced today on Rails main: rails/rails#50205 (comment)

[defkode]

@bensheldon Thanks!