fix(modules): fix IAM key delimiters, log filters, and conditions in custom modules

[aghassemlouei]

Description

Fixes logic defects, IAM key delimiter collisions, and conditional binding support across Stellar Engine custom modules (modules/cis-log-alerts, modules/cis-log-metrics, modules/intrusion-detection-system, modules/organization-se, and modules/spanner-instance-se), split out from #274:

• modules/cis-log-alerts: Exposes var.notification_channels and concatenates additional channels with the default email notification channel; uses each.key instead of the literal string "each.key" for alert condition display names.
• modules/cis-log-metrics: Fixes operator precedence parentheses in the project-owner-log CIS log filter expression.
• modules/intrusion-detection-system: Fixes inverted ternary (var.create_service_networking_connection ? 1 : 0) on google_service_networking_connection.private_vpc_connection.
• modules/organization-se: Uses // delimiter in iam-bpa:${principal}//${role} keys, wraps the comprehension in merge([...]) so empty maps do not fail, and anchors the organization_id validation regular expression (^organizations/[0-9]+$).
• modules/spanner-instance-se: Adds condition support to var.iam_bindings and google_spanner_instance_iam_binding.authoritative.
• tests/tools/test_blueprint_and_module_validations.py: Adds unit tests covering all five custom Stellar Engine modules.

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-3 (Access Enforcement), AC-6 (Least Privilege), AU-6 (Audit Record Review, Analysis, and Reporting), SI-4 (System Monitoring), SI-10 (Information Input Validation).

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

• Executed hclfmt across all five custom Stellar Engine modules.
• Executed python3 -m unittest discover -s tests/tools (35/35 unit tests passing, including test_custom_stellar_engine_modules_validations).

[Calvin-Cheng1]

lgtm