Kubeadm: Automate certificate copy between control planes in HA setups

- Joining control plane nodes to a HA cluster can now be simplified by enabling the optional automatic copy of certificates from an existing control plane node.
- You can now use `kubeadm init --experimental-upload-certs` and `kubeadm join --experimental-control-plane --certificate-key`.

- Mark Job onPodConditions as optional in pod failure policy ([#120209](https://github.com/kubernetes/kubernetes/pull/120209), [@mimowo](https://github.com/mimowo)) [SIG API Machinery and Apps]

### Feature

- Changed kuberc configuration schema. Two new optional fields added to kuberc configuration, `credPluginPolicy` and `credPluginAllowlist`. This is documented in [KEP-3104](https://github.com/kubernetes/enhancements/blob/master/keps/sig-cli/3104-introduce-kuberc/README.md#allowlist-design-details) and...

- Added new optional APIs in `ResouceSlice.Basic` and `ResourceClaim.Status.AllocatedDeviceStatus`. ([#130160](https://github.com/kubernetes/kubernetes/pull/130160), [@KobayashiD27](https://github.com/KobayashiD27)) [SIG API Machinery, Apps, Architecture, Node, Release,...

- The name of CEL(Common Expression Language) optional type has been changed from `optional` to `optional_type`. ([#124328](https://github.com/kubernetes/kubernetes/pull/124328), [@jiahuif](https://github.com/jiahuif)) [SIG API Machinery, Architecture, Auth, CLI, Cloud Provider, Network and Node]

- Property `conditions` in `apiextensions.v1beta1.CustomResourceDefinitionStatus` and `apiextensions.v1.CustomResourceDefinitionStatus` is now optional instead of required. ([#64996](https://github.com/kubernetes/kubernetes/pull/64996), [@roycaihw](https://github.com/roycaihw))

### ConfigMap
* Volumes and environment variables populated from ConfigMap and Secret objects can now tolerate the named source object or specific keys being missing, by adding `optional: true` to the volume or environment variable source specifications. ([#39981](https://github.com/kubernetes/kubernetes/pull/39981), [@fraenkel](https://github.com/fraenkel))

- Use omitempty for optional Job Pod Failure Policy fields ([#126046](https://github.com/kubernetes/kubernetes/pull/126046), [@mimowo](https://github.com/mimowo)) [SIG Apps]

### Bug or Regression

- Use omitempty for optional Job Pod Failure Policy fields ([#126046](https://github.com/kubernetes/kubernetes/pull/126046), [@mimowo](https://github.com/mimowo)) [SIG Apps]

### Bug or Regression

* Fix a potential bug that scheduler preempts unnecessary pods. ([#70898](https://github.com/kubernetes/kubernetes/pull/70898), [@Huang-Wei](https://github.com/Huang-Wei))
* The kube-apiserver's healthz now takes in an optional query parameter which allows you to disable health checks from causing healthz failures.  ([#70676](https://github.com/kubernetes/kubernetes/pull/70676), [@logicalhan](https://github.com/logicalhan))