fix(cli): inconsistent behavior across CLI flags, environment variables, and config files

[knqyf263]

Description

In a recent update to Trivy, we introduced validation and alias functionalities for CLI flags. However, we realized that these enhancements had not been uniformly applied to other configuration methods, specifically environment variables and the configuration file (trivy.yaml). This PR addresses this oversight by extending the validation and alias features across all configuration settings, ensuring consistency and improved usability.

To facilitate this integration, we've added a Parse() method. This method is designed to be called before accessing values through the Value() method, mirroring the interface pattern found in the Go's standard flag package (flag package documentation). This addition ensures that value retrieval does not result in errors and that the parsing process is streamlined across different settings.

Additionally, we've refactored the handling of default flag values. Previously, the logic was branched based on the type of the Default field of each flag. We've now shifted this approach to leverage Go's generics, allowing for a more explicit and type-safe representation of default values.

Related issues

• Close Inconsistent behavior of --scanners aliases across CLI flags, environment variables, and config files #5803

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[knqyf263]

@naortalmor1 @tonaim I believe it requires small changes on your end, but please let me know if it has a big impact. We'll consider another approach in that case.

[DmitriyLewen]

LGTM.
Left nit comment.

[knqyf263]

@naortalmor1 @tonaim No comments? Can I push on this change?