Add Terraform to this repo

Leverage the code files and agent instructions from this PR: https://github.com/Azure-Samples/azd-starter-terraform/pull/2 to recreate a new PR baselined on this new repo.

The goal is for this repo to closely match the base template (bicep), but add side-by-side Terraform files that can be used in an alternate azd up step, once the user alters the azure.yaml to point to the new terraform.

for now, nest the terraform IaC in this folder:
-> /infra <--bicep/default iac files
-->/infra-tf <-- terraform iac files nested inside /infra

alter the readme with an alternate deploy step where azure.yaml is changed, /infra/infra-tf is used