AWS Step Functions as a replacement for the Controller logic

[jseed]

AWS step functions did not exist when this project was first created. As a result, we had to come up with our own "state machine" implementation to manage the replication setup flow. This became the Controller function, which uses a dynamodb streams from a checkpoint table to manage and act on state. It is worth investigating wether or not this logic could be converted to AWS Step functions, and if this change would bring any benefits.