Preinstall SSM agent on AWS instances

[JedMeister]

It has come to my attention that AWS provide a System Manager (aka SSM) agent. It seems that that may provide value for TurnKey users on AWS. So we should consider installing it.

[JedMeister]

Looking closer at the AWS SSM agent, I'm not sure how much value this would give most of our users? So downgrading to "wishlist" and deferring for now.