Add the ability to migrate terraform state

[verbanicm]

TL;DR

Provide the ability for users to inform guardian that the state file needs to be migrated.

Detailed design

Use PR body comments to determine if the -migrate-state flag should be used in the terraform init command.

This would require two phases:

1. Checkout the main branch, run terraform init
2. Checkout the PR branch, run terraform init -migrate-state
   • This would leave the existing state intact, so if the plan/apply failed, it would be a no-op
3. Continue with the plan and apply

There should be a separate and distinct step to remove the old state file after a successful plan and apply.

Alternatives considered

No response

Additional information

No response