[DOCS] Manage resources with TF

[schavis]

Brings in the instructions from https://developer.hashicorp.com/well-architected-framework/operational-excellence/operational-excellence-migrate-unmanaged-vault-namespace-to-terraform-managed-infra#next-steps

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CI Results: All Go tests succeeded! :white_check_mark:

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Build Results: All builds succeeded! :white_check_mark:

[schavis]

Looks good! Just a few suggestions on updating the prompt from # to $ in a few places.

Thanks for catching that!