Request: add support for preemption

[tantrev]

For schedulers like SLURM, preemptible jobs are really nice. Many University computing resources have a lot of spare computing power for preemptible jobs and having functionality from future.batchtools to support them (and re-schedule them if anything went wrong) would be fantastic.

[HenrikBengtsson]

Yes, I agree, that would be very useful.

Being able to relaunch futures, in general, is a feature request that others asked about. I've started a specific issue on this over at futureverse/future#205.

Do you know if the underlying batchtools package provides mechanisms for working with preemptible jobs? I think that would be needed/very useful in order to start thinking about how this can be supported. It'll also help in identifying the API for futureverse/future#205.