Implement orchestration for workload account provisioning "layers"

[sheaphillips]

Describe the issue

Currently we have implemented a set of distinct automations - in the form of terraform modules - for applying several BC Gov-specific elements (layers) to AWS accounts to be used as project workload accounts within an SEA LZ. However, these modules are not "connected" and must be executed separately, and some manual steps are currently required to transfer outputs from one module to another. We need a "one-shot" mechanism to execute all the "layers". We have identified terragrunt as a tool to to support this approach and we need to complete the associated work to use it for provisioning workload account "layers".

Which Sprint Priority is this issue related to? The 'Milestone' should clearly list Sprint Priorities - which one is this issue related to?

Additional context This task should precede the work to migrate the execution to the managed runtime / state management environment

Definition of done

• A new GitHub repository with terragrunt code to invoke the various modules in the correct order, respecting dependencies, and transferring values between them
• updated bootstrap modules (as/if required) to function in the terragrunt driven approach
• documented steps to execute the bootstrapping process

[sheaphillips]

Note: This work was not specifically included in Sprint 15, but is partially establishing a pattern to be used in equivalent ticket for landing zone bootstrap code, so has been included.