Add --feature-gates flag to the k0s config subcommand

[twz123]

Description

This prevents a panic when validating an IPv6-only k0s config.

NB: CallPersistentPreRun has been resurrected from commit f977380.

Fixes:

• Unable to pass --feature-gates to k0s config validate #6611
• Implement k0s feature gates #6130

See:

• Encapsulate debug flag handling #5390

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

How Has This Been Tested?

• Manual test
• Auto test added

Checklist

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[k0s-bot]

Successfully created backport PR for release-1.34:

• [Backport release-1.34] Add --feature-gates flag to the k0s config subcommand #6619