Add asynchronous task running framework

[coollog]

No description provided.

[elharo]

Asynchronicity adds a lot of complexity and is very hard to get right. What's the use case?

[coollog]

A lot of the image pulling/building/pushing can be done in parallel, so this would run the steps that can be run in parallel in parallel. This would be an extra optimization that we add after everything works synchronously.

[loosebazooka]

Can we put this on the backburner until its use is obvious? The PR doesn't provide much context in its current form.

[coollog]

Yea, definitely. That PR is not ready for review yet. This should come after everything works synchronously.

[coollog]

Closing as this will be implemented in https://github.com/google/jib