Fix various issues in the distro validation script

[Blue (OneBlue)]

Summary of the Pull Request

This change solves various issues that cause the distro validation script not to detect enabled system units correctly.

This change also adds more unit to the discouraged list

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

This PR updates the modern distro validation script to improve detection of enabled systemd units from the distro tarball and expands the set of discouraged systemd units.

Changes:

• Added systemd-vconsole-setup.service to the discouraged system unit list.
• Reworked systemd enabled-unit discovery to better resolve symlinks and normalize tar paths.