Update and document code copied from Kubernetes repository

[dgrisonnet]

A lot of code was copied from upstream k/k, but it is not documented which file/functions are and they have hardly been updated since. To make it easier and maybe fix a few bugs, it would be great to update and document them.

[k8s-triage-robot]

This issue has not been updated in over 1 year, and should be re-triaged.

You can:

• Confirm that this issue is still relevant with /triage accepted (org members only)
• Close this issue with /close

For more details on the triage process, see https://www.kubernetes.dev/docs/guide/issue-triage/

/remove-triage accepted

[dashpole]

/triage accepted