fix(stages,blueprints): remove unused dead variables from 3-security and postgresql

[aghassemlouei]

Description

This pull request cleans up declared variables that are never referenced by resources, data sources, or locals:

• Fixes [Bug] il5/postgresql: dead variables (core_project_id, google_compute_global_address_name, subnetwork_name) #112: Removes unused variables core_project_id, google_compute_global_address_name, and subnetwork_name from the PostgreSQL blueprint (variables.tf, terraform.tfvars.sample, and README.md).
• Fixes [Bug] 3-security: variable tenant_accounts is declared but never referenced (dead variable at the stage level) #113: Removes unused variable tenant_accounts from FAST Stage 3-security (variables.tf and README.md).

Fixes #112
Fixes #113

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: N/A

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/ can be leveraged for this change.
• My code follows the established naming conventions outlined in documentation/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, IL5, etc.).

Testing

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

Testing Performed

• Validated variable definitions across blueprints/il5/postgresql and fast/stages-aw/3-security.
• Confirmed documentation variables tables match actual declared variables.

[aghassemlouei]

@mgcarey-google would like someone else to take a peek at this. Adding additional reviewers and assignees.

[Calvin-Cheng1]

Agree with #112. Those are dead variables.

For #113 while these variables are unused in security.tf, they are intended to be available and consumable in case there are modules/resources in stage 3 that require any previous outputs from 0-bootstrap, 1-resman, or 2-networking. I would prefer to keep them

[Calvin-Cheng1]

LGTM after some changes