ci: Implement Policy as Code Checks

[carlagesa]

To enforce organizational standards and security compliance automatically, we should introduce Policy as Code (PaC). Tools like Open Policy Agent (OPA) or Sentinel can be integrated into the CI/CD pipeline to check the Terraform plan against a predefined set of rules (e.g., disallowing public S3 buckets, enforcing specific instance types). This adds a critical layer of automated governance.
Acceptance Criteria:

A Policy as Code tool (e.g., OPA) is chosen and integrated into the CI pipeline.
At least one basic policy is written (e.g., ensure all S3 buckets have logging enabled).
The pipeline generates a Terraform plan and validates it against the policy set.
The pipeline fails if the plan violates any of the defined policies.