Implement a background job shard

I'm converting what used to be a 1.0 roadmap note into an issue so that we can have a bit more discussion but still track it on the Roadmap board. I don't think you can link discussions to projects, but we can always convert this to a discussion if it gets too "busy".

Paul linked a gist showing how we might accomplish something sort of similar to ActiveJob in Rails, where there's a common API you can "hook into" easily:
https://gist.github.com/paulcsmith/7ee1bd36d4738518f779951239226537

That said, I wonder if this is really something we need for a 1.0 release, or if we could just rely on something like Sidekiq or Mosquito more heavily with tutorials/community content.

My experience is that while yes, ActiveJob does have its uses, a high-performing job queue like Sidekiq implements its own way of doing things and recommends against using the ActiveJob interface.

Start by reading the linked gist and the discussion about an ActiveJob-like API, then compare the stated tradeoffs with Sidekiq and Mosquito. The issue does not identify files, tests, an entry point, or settled acceptance criteria; scope and whether this belongs in the 1.0 release must be decided before implementation can be considered done.