Heads up: Go workspaces, kube 1.30, and k8s.io/code-generator breakage

[Tim Hockin]

Hi everyone. I wanted to broadcast some in-progress work to a) warn
people about it; and b) get feedback on potential impact.

KEP 4402 (https://github.com/kubernetes/enhancements/tree/master/keps/sig-architecture/4402-go-workspaces)
will add support for Go Workspaces to k/k. The TL;DR is that all
sorts of tooling and build stuff gets simplified, tons of code is
removed.

So why is this a "warning" ?

Many of our code-generation tools (everything built on gengo) will
break. This change, unfortunately, makes some of the hacks that
gengo-tools use stop working. The silver lining is that they _barely_
work today (anyone who uses them outside of k/k knows).

In Kube v1.28 we deprecated the `generate-groups` scripts from
k8s.io/code-generator
(https://github.com/kubernetes/kubernetes/pull/117897). This change
will break them completely. The replacement script (kube_codegen.sh)
should still work, but has some CLI changes needed.

If you depend on generate-groups or kube_codegen, or if you call tools
like client-gen yourself -- please take note. I would appreciate to
hear from you.

My WIP PR for k/k: https://github.com/kubernetes/kubernetes/pull/122624

Tim