feat(validations): Add early required validation

[AdarshK15]

Summary

This PR introduces the required validator to the module-scoped validation framework. It allows enforcing the presence of mandatory settings or explicitly forbid specific settings (e.g., for deprecation) directly within metadata.yaml. By moving these checks into the metadata layer, these constraints are validated earlier in the deployment lifecycle.

Key Changes

New RequiredValidator: Implements a validator to enforce the presence or absence of module settings.

Functionality:

• Required (Default): Validates that all variables in the provided list are "set".
• Forbidden: When configured with forbidden: true, validates that none of the specified variables are "set". This is
  useful for preventing the use of deprecated variables or enforcing "must not be set" constraints.
• Active: A variable is considered "set" if it is a non-empty string, a non-zero number, a true boolean, or a
  non-empty collection (list/map).

Testing

Added unit tests in pkg/validators/metadata_validators_test.go covering:

• Pass/Fail scenarios for missing required variables.
• Pass/Fail scenarios for present forbidden variables.

Documentation

Updated docs/blueprint-validation.md to include usage instructions and YAML examples for both enforcing required
variables and forbidding unwanted ones.

[gemini-code-assist]

Summary of Changes

Hello @AdarshK15, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the module-scoped validation capabilities by introducing a versatile 'required' validator. This new validator allows module authors to define precise constraints on input variables within their metadata.yaml files, ensuring that configurations meet necessary criteria or avoid deprecated settings. By integrating these checks earlier in the deployment process, the change aims to improve the robustness and reliability of module deployments.

Highlights

• New RequiredValidator: Introduced a new RequiredValidator to the module-scoped validation framework, enabling enforcement of mandatory or forbidden settings directly within metadata.yaml files.
• Flexible Validation Logic: The RequiredValidator supports two modes: 'required' (default) to ensure variables are set, and 'forbidden' to ensure variables are not set (useful for deprecation). A variable is considered 'set' if it's a non-empty string, non-zero number, true boolean, or non-empty collection.
• Expanded Validation Coverage: Applied the new required validator to various metadata.yaml files across different modules to enforce the presence of critical variables (e.g., instance_image.project, zone) and to explicitly forbid deprecated variables (e.g., enable_smt, disable_smt, scopes, job_template_contents).
• Comprehensive Testing: Added unit tests for the RequiredValidator in pkg/validators/metadata_validators_test.go, covering pass/fail scenarios for both required and forbidden variables, as well as custom error messages.
• Updated Documentation: The docs/blueprint-validation.md file has been updated to include detailed usage instructions and YAML examples for the new RequiredValidator, demonstrating how to enforce required variables and forbid unwanted ones.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable required validator, which is effectively used across several modules to enforce required settings and deprecate old ones. The implementation is solid, but I've identified a couple of logic issues in the new helper functions that could lead to incorrect validation behavior in edge cases. Specifically, the logic for determining if a variable is 'set' needs refinement for empty collections and numeric zero values. I've also noted a minor formatting issue in an error message. The accompanying documentation and test cases are a great start.

[AdarshK15]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a valuable required validator, enhancing the module validation framework. The implementation is solid, with comprehensive tests and clear documentation. I've suggested one refactoring in pkg/validators/metadata_validators.go to improve code consistency and maintainability by leveraging an existing helper function, which aligns with our goal for technical excellence and maintainable code.