Flatten TF module structure via .tfvars/.tfbackend, update to TF v1.5.3

[GaryGSC]

Using .tfvars and .tfbackend files, we can flatten our TF modules.

Before	After

[GaryGSC]

This module restructuring clobbers the existing state, but I don't really want to fill up the template with a bunch of moved blocks.

[GaryGSC]

As an example of how to use these environments, navigate to the terraform/app directory and then:

• aws sso login
• terraform init -backend-config=dev.s3.tfbackend
• terraform plan -var-file=dev.tfvars

---

If you then try switch to production (not that you should really be doing that outside of CI/CD), the CLI will instruct you to call terraform init with either the -migrate-state or -reconfigure. -reconfigure is the correct option here because you're not trying to migrate our dev state to prd. So, it'd look like:

• aws sso login (but to the prd account this time)
• terraform init -backend-config=prd.s3.tfbackend -reconfigure
• terraform plan -var-file=prd.tfvars

[GaryGSC]

Rebased on dev.

[stuft2]

@jvisker have we talk about this in the cloud guild yet? Are we still discussing it? Do we need to update an ADR before merging?

[GaryGSC]

Updated docs. That needed to happen.

Also renamed terraform-iac/ to terraform/. We're restructuring our TF stuff anyways, so this seemed like a good opportunity to also rename the directory. Why? Calling the directory terraform/ is common enough in the industry that themes can pick up on that (e.g. in VSCode or Chrome):

[GaryGSC]

Another tiny reason to rename terraform-iac to terraform: editors treat kebab-case as multiple "words" and so the directory name can't be selected by double-clicking.