Automatic merge from submit-queue
kubeadm: Implementing the controlplane phase
**What this PR does / why we need it:**
This contains implementation of controlplane phases in kubeadm, which is part of the wider effort of implementing phases in kubeadm, previously in alpha stage.
The original proposal for this activity can be found [here](https://github.com/kubernetes/kubeadm/pull/156/files) and related comments.
Kubeadm phase implementation checklist is defined [here](https://github.com/kubernetes/kubeadm/issues/267)
Common implementation guidelines and principles for all phases are defined [here](https://docs.google.com/document/d/1VQMyFIVMfRGQPP3oCUpfjiWtOr3pLxp4g7cP-hXQFXc/edit?usp=sharing)
This PR implements:
- [x] kubeadm phase controlplane: wip by @fabriziopandini
- [x] kubeadm phase controlplane all
- [x] kubeadm phase controlplane etcd
- [x] kubeadm phase controlplane apiserver
- [x] kubeadm phase controlplane scheduler
- [x] kubeadm phase controlplane controller-manager
**Which issue this PR fixes:**
https://github.com/kubernetes/kubeadm/issues/349
**Special notes for your reviewer:**
This PR implements the same approach of #49419, thus minimising rework/impacts on existing codebase.
- Factor out token constants to kubeadmconstants.
- Move cmd/kubeadm/app/util/{,token/}tokens.go
- Use the token-id, token-secret, etc constants provided by the bootstrapapi package
- Move cmd/kubeadm/app/master/tokens.go to cmd/kubeadm/app/phases/token/csv.go
This refactor basically makes it possible to hook up kubeadm to the BootstrapSigner controller later on
