Merge pull request #46254 from mtaufen/dkcfg

Automatic merge from submit-queue (batch tested with PRs 50016, 49583, 49930, 46254, 50337)

Alpha Dynamic Kubelet Configuration

Feature: https://github.com/kubernetes/features/issues/281

This proposal contains the alpha implementation of the Dynamic Kubelet Configuration feature proposed in ~#29459~ [community/contributors/design-proposals/dynamic-kubelet-configuration.md](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/dynamic-kubelet-configuration.md). 

Please note:
- ~The proposal doc is not yet up to date with this implementation, there are some subtle differences and some more significant ones. I will update the proposal doc to match by tomorrow afternoon.~
- ~This obviously needs more tests. I plan to write several O(soon). Since it's alpha and feature-gated, I'm decoupling this review from the review of the tests.~ I've beefed up the unit tests, though there is still plenty of testing to be done.
- ~I'm temporarily holding off on updating the generated docs, api specs, etc, for the sake of my reviewers 😄~ these files now live in a separate commit; the first commit is the one to review.

/cc @dchen1107 @vishh @bgrant0607 @thockin @derekwaynecarr 

```release-note
Adds (alpha feature) the ability to dynamically configure Kubelets by enabling the DynamicKubeletConfig feature gate, posting a ConfigMap to the API server, and setting the spec.configSource field on Node objects. See the proposal at https://github.com/kubernetes/community/blob/master/contributors/design-proposals/dynamic-kubelet-configuration.md for details.
```

pkg/api/types.go

@@ -2913,6 +2913,19 @@ type NodeSpec struct {
 	// If specified, the node's taints.
 	// +optional
 	Taints []Taint
+
+	// If specified, the source to get node configuration from
+	// The DynamicKubeletConfig feature gate must be enabled for the Kubelet to use this field
+	// +optional
+	ConfigSource *NodeConfigSource
+}
+
+// +k8s:deepcopy-gen:interfaces=k8s.io/apimachinery/pkg/runtime.Object
+
+// NodeConfigSource specifies a source of node configuration. Exactly one subfield must be non-nil.
+type NodeConfigSource struct {
+	metav1.TypeMeta
+	ConfigMapRef *ObjectReference
 }
 
 // DaemonEndpoint contains information about a single Daemon endpoint.