Add Autoscaling DynamoDB table shortcut

[drboyer]

Auto-scaling DynamoDB tables are neat - they enable you to handle scaling workloads with DynamoDB without losing money overprovisioning your table, and can be more cost effective than by-request pricing in some cases. Unfortunately, they're kinda a pain to set up - they require including several additional resources, including IAM roles.

It'd be nice to have a cloudfriend shortcut which can handle generation of the scaling scaffolding for you, exposing just the min/max and scaling threshold parameters needed to configure autoscaling.