Support local state for a phased bootstrap of launchpad

Hi,

We work on a launchpad configuration with Azure Storage Account as backend. We want to use storage account encryption with customer managed keys. This requires a phased deployment / bootstrap of a new launchpad, where managed identity, keys and role assignment is created in phase 1, and storage accounts and blobs are created in phase 2.

For phase1 we don't have any backend storage available so this will not work with the Rover. Is it possible to implement support for local backend with Rover to support a phased deployment of a new launchpad. Is should also be easy to migrate the local state files to the storage accounts when they become available in phase 2.

The issue names no files, tests, or entry points. Begin by locating Rover's backend-state handling and verify how a local phase-one state could transition to Azure Storage in phase two; done means phased bootstrap works without an initial remote backend and local state can be migrated.

Written by the indexing model from the issue text.