Change operator project structure to multi-group

In order to better integrate with kube client codegen, we need to change our project structure to support "multi-group". That's the way we used to have in the past.

So instead of `api/[version]` we will have `apis/[group]/[version]`. This is the layout expected by k8s client codegen tooling. Won't impact any customers or users since we won't change any interfaces.

To know more about multi-group projects, see:

https://book.kubebuilder.io/migration/multi-group.html

It also have the possibility to migrate to a new group in the future since the default `app` we have today might not be suitable for our use case.