Consolidate multiple Terraform deployments into a single Terraform deployment

[brooke-hamilton]

Benefit/Result/Outcome
So that I can have a simplified deployment experience, and to simplify automatic cleanup of resources.

Description
The hub, T0, T1, and T2 are all separate Terraform deployments with separate state management. They are unified through shell scripts that set up the service principal, key vaults, and storage accounts for state management. The scripts also execute the deployments in order. The work described in this issue is to have a single Terraform deployment for the hub, T0, T1, and T2. Also, in scope is to move logic from the shell scripts into Terraform for setting default parameter values, setting up key vaults and storage accounts, and any other logic that can be performed in Terraform.

Acceptance Criteria

• A single main.tf drives the deployment.
• Script logic is simplified and moved to Terraform where possible.
• The script arguments remain the same.
• Consider including Allow users to bring their own credential for deployment #176 as part of the scope of this work if simpler than doing it separately.
• Update the user interface to work with the new Terraform deployment.