Move kubelet config file into run directory

[twz123]

Description

This is generated at runtime and doesn't need to be part of the persistent data directory. Group private kubelet fields together, to have a better overview which fields are used by the external configuration versus the internal state. Rename dataDir to rootDir to reflect that it's the kubelet's root directory and not k0s's data directory.

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 own 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