We should support generate CRDs in scripts like kubebuilder

[zhaojizhuang]

We should support generate CRDs in scripts like kubebuilder or using kubebuilder

https://book.kubebuilder.io/reference/generating-crd.html

[zhaojizhuang]

cc @n3wscott @grantr

[n3wscott]

We have the start of a tool, in use:

• Schema tool for Eventing v1 eventing#5087
• Adding integration with the kn/pkg schema cli for the Discovery repo. knative-extensions/discovery#153

[dan-j]

Given this is standard practice for Operator SDK projects, in the meantime, would it make sense to add a section in the documentation/README.md titled "CRD Generation", and give contributors instructions on the current process, whether that be, "you create/update CRDs manually, here's some tools to help you do it", or whatever.

I've lost a good part of a day reading through the hack repository and other scripts within github.com/knative-sandbox/eventing-natts to be told via Knative Slack that CRDs aren't generated.

Happy to contribute this documentation, but I don't actually know what the process is yet. My next steps are to dig around #5087 but haven't got round to it yet.