[huong8373tt-beep]

Description

Fixes #317.

var.notebooks[each.key].owner is a string, whereas google_workbench_instance.playground expects instance_owners to be a list(string). Calling try(tolist(var.notebooks[each.key].owner), null) in blueprints/fedramp-high/vertex-mlops/vertex.tf failed type conversion on strings and always evaluated to null. This change passes null when owner is unset and [var.notebooks[each.key].owner] when configured, and documents the optional owner setting for USER_MANAGED notebooks in README.md and terraform.tfvars.sample.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Deployment & Compliance Impact

• Applicable Regimes:
  • US Region Restricted (e.g., Access Policy constraint)
  • FedRAMP Moderate
  • FedRAMP High
  • DoD IL4
  • DoD IL5
  • General / All
• NIST 800-53r5 Controls: AC-2, AC-3

Checklist

Code Quality & Reusability

• My code adheres to the Maximize Reusability principle. I have not redefined common elements and have reused existing base configurations and modules where possible.
• I have checked that no existing module or configuration in modules/ or fast/stages-aw/ can be leveraged for this change.
• My code follows the established naming conventions outlined in docs/naming-convention.md.

Documentation

• I have updated the README.md of the modified module or blueprint.
• I have added/updated documentation for inputs (variables) and outputs.

Security

• My change adheres to GCP security best practices and the principle of least privilege.
• I have ensured compliance with the targeted regime (FedRAMP Moderate, FedRAMP High, IL4, IL5, etc.).

Testing

• I have tested my changes locally.
• I have included details of my testing in this PR.

Testing Performed

• Executed bash tools/run_tests.sh and bash tools/lint.sh.
• Verified with terraform init and terraform plan in blueprints/fedramp-high/vertex-mlops that google_workbench_instance.playground resolves instance_owners to [<owner>] when owner is set and null when omitted.

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[aghassemlouei]

Thanks for catching and fixing the Workbench owner list conversion in vertex-mlops, @huong8373tt-beep! Validated the plan output and this looks good to merge.