Serverless table copy

[jseed]

Currently, copying/backfilling the replica for an existing table is left to the user. Although this is ideally only a one time operation, it remains tedious, and complicates the initial deployment/setup of replication.

All of the existing solutions for copying tables appear to be long running tasks, requiring ecs clusters or other server infrastructure. Since we wanted our solution to remain "serverless", and could be executed manually prior to enabling replication, this was deemed out of scope for our initial solution.