Warn on unapplied migrations

[JoeSouthan]

Hi,

We use dependabot and will merge patch and minor version bumps automatically when specs pass. During investigation of #1358, we noticed we had some unapplied migrations.

Would adding something that checks the latest applied migration and either warns or raises if not applied, be something that would be useful?

Prior art:

https://github.com/que-rb/que/blob/80d6067861a41766c3adb7e29b230ce93d94c8a4/lib/que/migrations.rb#L74
https://github.com/flippercloud/flipper/blob/5aa9cfda77504922f5a95c50edc3410d6bfc1986/lib/flipper/adapters/active_record.rb#L289

Happy to implement this if so!

[bensheldon]

There is GoodJob.migrated? which returns true/false if there are pending/unapplied migrations for GoodJob.

It's mentioned in the "Upgrading minor versions" section of the Readme, but is totally overlookable 🤗

[JoeSouthan]

Sorry, missed that, appreciate the push in the right direction! 🤦