Allow replacing the scheduled execution time of a unique job

[monteithpj]

This commit adds the capability to update the scheduled execution time of a unique job, similar to :replace_args

Not sure whether this is the nicest way of going about it (if there are other fields that could be replaced in future, this API gets a bit messy) but just went with something very simple to spark discussion.

Any feedback gratefully received 😅

[sorentwo]

Thanks for opening the PR. This is an interesting use case and it prompts the question: what other things should be replaceable? What about meta, or tags, or priority, etc? I think the API needs to be flexible to support anything that is normally set in Worker.new, otherwise we'll slowly create toward a slough of replace_ keys. WDYT?

[monteithpj]

Yeah, that's what I was thinking. I can update to create something like:
Worker.new(args, replace: [:args, scheduled_at])

Would all the options other than :unique, :replace_args and schedule_in would make sense to be replaceable?

[sorentwo]

That replace syntax looks good!

Would all the options other than :unique, :replace_args and schedule_in would make sense to be replaceable?

Yes, exactly. We can also soft deprecate the replace_args variant and translate that into replace: [:args] internally.

[sorentwo]

This looks great, nicely done! One small suggestion that will simplify the replace_args support, otherwise this is good to go.

[sorentwo]

This is great! Thanks for working with me on it 💛