📝 Docs/cost metrics per account

[ASTRobinson]

A reference to the issue / Description of it

Documentation for #7170

How does this PR fix the problem?

Updates cost metrics documentation for per account_id functionality

How has this been tested?

Please describe the tests that you ran and provide instructions to reproduce.

locally tested in vscode.

Deployment Plan / Instructions

Will this deployment impact the platform and / or services on it?

No - Documentation only.

Checklist (check x in [ ] of list items)

• I have performed a self-review of my own code
• All checks have passed
• I have made corresponding changes to the documentation
• Plan and discussed how it should be deployed to PROD (If needed)

Additional comments (if any)

{Please write here}

[github-actions]

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Setting default tflint config...
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Installing "terraform" plugin...
Installed "terraform" (source: github.com/terraform-linters/tflint-ruleset-terraform, version: 0.9.1)
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[dms1981]

LGTM - love the animated images!