Refactor backup pipeline to use commands
In order to implement incremental backups we will be adding more operations than just Create/Restore but once we add these operations it would become difficult to also keep concurrency. So instead we encapsulate the execution of these operations into commands.
The objective here is to allow us to add CreateIncremental with concurrency, without duplicating a bunch of concurrency code.
Since this refactor makes it easy, I've gone ahead and added concurrency to restore.
Edited by James Fargher