✨ Rebase to Kubernetes 1.26

[ncdc]

Links:

• 1.24 branch commit tracking spreadsheet
• Pre-rebase prep branch (squashing as much as possible to minimize rebase effort; force-pushes will be frequent)

### Tasks
- [ ] https://github.com/kcp-dev/code-generator/pull/80
- [ ] Update our apimachinery to 1.26
- [ ] Update our client-go to 1.26

[ncdc]

apimachinery prep branch: https://github.com/kcp-dev/apimachinery/tree/1.26-prep

[ncdc]

client-go prep branch: https://github.com/kcp-dev/client-go/tree/1.26-prep

[nikhita]

This can now be closed, right?

cc @sttts

[xrstf]

This had been completed. We're now already on 1.28.