Integrate spacelift into AWS control tower account factory module

Currently, AWS’s terraform-aws-control_tower_account_factory module is configured to use Terraform Cloud/Enterprise (TFC/TFE) or the open-source Terraform Community Edition as the backend for the workspaces required to provision resources. This module simplifies Control Tower account provisioning by providing a large amount of infrastructure out of the box, which makes the process much easier.

With a few relatively minor adjustments, the module could instead be adapted to use Spacelift stacks as the backend for managing those workspaces.