Add support for the `async` Active Job backend used by default in Rails

[rosa]

Mostly so that this can be run in development, even if it's not super useful.

[matiassalles99]

What's the expected behavior with the async Active Job adapter? From what I saw it doesn't support most (if not any) of the features, it seems to work with one queue only but it has no name, and you can only access the number of completed jobs.

I might be wrong but those were my main takeaways from looking into the async adapter source code, and I just want to fully understand the expected behavior before working on the integration with mission-control :)