Extra arguments from K0S_EXTRA_ARGS in service startup

[kke]

Description

This was talked about at some point. This will make the service script installed by k0s install read extra arguments from K0S_EXTRA_ARGS.

This can be defined in:

• /etc/conf.d/k0s{{role}}] in openrc
• /etc/default/k0s{{role}} in sysv
• /etc/sysconfig/k0s{{role}}.conf in upstart
• /etc/systemd/system/k0s{{role}}.env in systemd

Darwin launchd is not modified as it would require some kind of a wrapper and k0s doesn't work there to begin with.

The systemd template was moved into its own file from service.go like all the others are.

Type of change

• [ ] Bug fix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [X] 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