Validate that workspace name aligns with var.assessment_account_name value

[dav3r]

🗣 Description

This PR adds an additional check to validate that the value in var.assessment_account_name aligns with the currently-selected workspace name (6ad9330).

Additionally, this PR updates the terraform_apply.sh script so that all of the validation checks of user-supplied data in assessment_validation.tf are performed before any other changes are applied (43126de).

Also note that part of 1b6f8b5 includes a documentation verbiage change (from terraform-docs) that was overlooked during #240.

💭 Motivation and context

We are constantly striving to find ways to reduce human error in our processes. This change should prevent errors where a COOL environment administrator accidentally uses a Terraform variables (tfvars) file meant for a different workspace.

Resolves #241.

🧪 Testing

I tested terraform plan, terraform apply, and terraform_apply.sh by supplying a tfvars file meant for a different COOL workspace. In each case, I got an error message like this:

Error: Resource precondition failed
│ 
│   on assessment_validation.tf line 15, in resource "null_resource" "validate_assessment_account_name_matches_workspace":
│   15:       condition     = replace(replace(lower(var.assessment_account_name), "/[()]/", ""), " ", "-") == terraform.workspace
│     ├────────────────
│     │ terraform.workspace is "env123-production"
│     │ var.assessment_account_name is "env456 (Production)"
│ 
│ Assessment account name (env456 (Production)) does not align with the currently-selected workspace (env123-production).  Are you sure that you are using the correct tfvars file?

I also verified that when I used the correct tfvars file for my workspace, the error above was not displayed.

All automated tests pass.

✅ Pre-approval checklist

• This PR has an informative and human-readable title.
• Changes are limited to a single goal - eschew scope creep!
• All relevant type-of-change labels have been added.
• I have read the CONTRIBUTING document.
• These code changes follow cisagov code standards.
• All relevant repo and/or project documentation has been updated
  to reflect the changes in this PR.
• All new and existing tests pass.

✅ Post-merge checklist

• Notify COOL environment administrators about this new validation.

[mcdonnnj]

[jsf9k]

Approved, with one suggestion that you can take or leave.