Automatic merge from submit-queue (batch tested with PRs 41146, 41486, 41482, 41538, 41784)

client-gen: independent scheme for clientsets

This PR adds a clientset internal scheme instead of using `pkg/api.Scheme`. **The clientset API stays the same.**

In detail:

- introduce a scheme for each clientset, i.e. do not use `pkg/api.Scheme+Registry+Codec+ParameterCodecs`.

  This makes it easier to compose client-go's clientset (which is rewritten in `staging/copy.sh` and therefore hardcoded to use `k8s.io/client-go/pkg/api.Scheme+Registry+Codecs+ParameterCodecs`) with third-party clientsets (kube-aggregator, openshift, federation) which are not rewritten using `copy.sh` as all of them are self-contained and therefore relocatable.

  This fixes https://github.com/kubernetes/kubernetes/pull/41403/files#diff-76edfb07dee54ff7ddeda25c33c10d29R81 and prepares client-gen for use in OpenShift.

- register types into the clientset scheme via `AddToScheme` for versioned clientsets. This decouples the client-go clients from announce+registration (internal clients continue using announce+registry and apigroup installers).

  This reduces complexity for client-go, possibly remove the necessity for the announce+register machinery for many use-cases, maybe even to delete it mid-term.
- port federation and testgroup  `install/install.go` to `announced.GroupMetaFactory` in order to have a proper `Install.Install(...)` func for registration.

With the first change it's easy to add the types of one clientset to the scheme of the other using the `clientset/scheme.AddToScheme` method. This allows to use cross-clientset `runtime.RawExtensions`:

```golang
import (
     "k8s.io/client-go/kubernetes"
     clientsetscheme "k8s.io/client-go/kuberentes/scheme"
     aggregatorclientsetscheme "k8s.io/kube-aggregator/pkg/client/clientset_generated/clientset/scheme"
)

kclientset, _ := kubernetes.NewForConfig(c)
aggregatorclientsetscheme.AddToScheme(clientsetscheme.Scheme)
```
Kubernetes types with a `RawExtension` can en/decode aggregator types after this.

TODO:
- [x] fix fake clientsets
- [x] get the `*Options` types registered correctly for core, compare DO-NOT-MERGE commit.
- [x] get prefered version right in internal client. Do we need all versions registered in the internal client to support negotiation?
- [x] run `staging/copy.sh` and run tests: https://github.com/kubernetes/kubernetes/pull/41744
- ~~[ ] fixup usage through-out the code-base~~
- **Follow-up**: move `import_known_versions.go` files somewhere such that import of the `api.Scheme` package automatically installs the apigroups. It looks like we depended on the import fo the clientset for this purpose.