Renames the control plane label

[ciroque]

This accommodates the change made in v1.20 which became the standard in 1.24.

This will require users to have Kubernetes v1.24 or higher; while NLK will run on lower versions, the control plane Nodes will not be excluded.

Closes #187

Proposed changes

Describe the use case and detail of the change. If this PR addresses an issue on GitHub, make sure to include a link to that issue using one of the supported keywords here in this description (not in the title of the PR).

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• I have updated any relevant documentation (README.md and CHANGELOG.md)