Use managed-execution in all stacksets

[nkraemer-sysdig]

Creating a aws_cloudformation_stack_set_instance that deploys to multiple regions in paralell is not yet possible due to hashicorp/terraform-provider-aws#24752, however using the managed-execution flag on the aws_cloudformation_stack_set resources allows multiple aws_cloudformation_stack_set_instance resources to be created in parallel. This has a similar effect, although more objects must be created, potentially neccesitating a higher -parallelism flag on terraform apply.

This PR enables managed-execution for all stacksets created.

Manual testing for a 4 account org, 5 regions, CSPM + EventBridge:

• TF parallelism=10, managed-execution=false

  • Start: 4:05 (destroy: 4:27)
  • End: 4:27 (destroy: 4:40)
  • Duration: 22m (destroy: 13m)

• TF parallelism=10, managed-execution=true

  • Start: 4:40 (destroy: 4:46)
  • End: 4:46 (destroy: 4:49)
  • Duration: 6m (destroy: 3m)

• TF parallelism=100, managed-execution=true

  • Start: 4:50 (destroy: 4:55)
  • End: 4:55 (destroy: 4:57)
  • Duration: 5m (destroy: 2m)

[cgeers]

👍 well done.