[ECS] SpotInstanceDraining Agent Configuration

[mkulke]

What I'd like:

I need to be able to set this parameter to true via user data, to evict workload safely from to-be-terminated spot instances in my cluster

Any alternatives you've considered:

This agent functionality could be implemented in bottlerocket (see https://github.com/reach-now/spot-termination-handler), but I would not see a good reason why this would be preferable.