docs: Add concise docs on how to use terraform/modules

Created by: efritz

How to:

• tfenv
• set versions
• log into google or aws
• how to tf init, setup provdiers, etc

Seems like there's 2 ways to auth, need to pick one:

• Either via GOOGLE_APPLICATION_CREDENTIALS
• Or using "application default credentials" https://registry.terraform.io/providers/hashicorp/google/latest/docs/guides/provider_reference#credentials