Support spot instances

[mikemhenry]

It would be nice to support spot instances, as a first step I would be happy if the job just failed if it was killed, but it would be really nice if it tried N times if it gets evicted before it cancles the job.

[ethanholz]

I think this is a great idea and one we could support but may not be a priority for us in the short term. I am interested in at least documenting how that would need to work in then 'start-aws-gha-runner' repo. At a base level this should be pretty easy to implement for the first case you describe, but might be more complicated to implement a retry state as it currently stands.