Move to k8s.io/code-generator/kube_codegen.sh for codegen

Expected Behaviour

We need to move to using k8s.io/code-generator/kube_codegen.sh instead of generate-groups.sh

I don't know what that involves, but here's the output from codegen now:

>> Using /home/alex/go//pkg/mod/k8s.io/code-generator@v0.28.3
>> Temporary output directory /tmp/tmp.DO0QQSXUdS
WARNING: generate-groups.sh is deprecated.
WARNING: Please use k8s.io/code-generator/kube_codegen.sh instead.

WARNING: Specifying "all" as a generator is deprecated.
WARNING: Please list the specific generators needed.
WARNING: "all" is now an alias for "applyconfiguration,client,deepcopy,informer,lister"; new code generators WILL NOT be added to this set

WARNING: generate-internal-groups.sh is deprecated.
WARNING: Please use k8s.io/code-generator/kube_codegen.sh instead.

Generating deepcopy funcs
Generating apply configuration for openfaas:v1 iam:v1 at github.com/openfaas/faas-netes/pkg/client/applyconfiguration
Generating clientset for openfaas:v1 iam:v1 at github.com/openfaas/faas-netes/pkg/client/clientset
Generating listers for openfaas:v1 iam:v1 at github.com/openfaas/faas-netes/pkg/client/listers
Generating informers for openfaas:v1 iam:v1 at github.com/openfaas/faas-netes/pkg/client/informers
>> Removing /tmp/tmp.DO0QQSXUdS

It may help to look at what @stefanprodan is doing in Flagger/Flux

https://github.com/fluxcd/flagger

Why is this needed?

For continued compatibility