Rewrite the Terraform recipe overview documentation #1436

Describe the bug

Rewrite the Terraform recipe overview documentation to explain in detail how to author a Terraform recipe including:

What module storage options Radius supports (generic Git)
How to reference a Terraform configuration when registering a recipe (git::https://github.com//.git//directory/sub-directory
What Terraform backend options Radius supports (Kubernetes)
Other technical detail for Terraform practitioners

AB#15841