Keep the old names when generating admin kubeconfigs

[twz123]

Description

Of course, the initial assumption that nothing should rely on the actual names of the cluster, auth info and context in the admin kubeconfig was wrong: k0sctl relies on them and will panic if the admin kubeconfig has a different structure.

Use the old names again for them. Those aren't that important anyways, and it doesn't make sense to introduce a breaking change for this.

See:

• Handle unexpected names in the kubeconfig k0sctl#1087

Fixes:

• Build admin kubeconfig directly from PKI files #7600

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