Merge pull request #30798 from smarterclayton/fix_kubeconfig

Automatic merge from submit-queue

Allow a flag that forces kubelet to have a valid kubeconfig

`--require-kubeconfig` forces the kubelet to use the kubeconfig for all
APIserver communication, and exit cleanly.  Allows cluster lifecycle to loop waiting for config to be available.

Fixes #30515

A follow up PR will handle the issue discovered where the DefaultCluster rules applied to kubeconfig allow a malicious party who can bind to localhost:8080 to take advantage of an admin misconfiguration.

@lukemarsden @mikedanese



```release-note
The Kubelet now supports the `--force-kubeconfig` option which reads all client config from the provided `--kubeconfig` file and will cause the Kubelet to exit with error code 1 on error.  It also forces the Kubelet to use the server URL from the kubeconfig file rather than the  `--api-servers` flag.  Without this flag set, a failure to read the kubeconfig file would only result in a warning message.

In a future release, the value of this flag will be defaulted to `true`.
```

hack/verify-flags/known-flags.txt

@@ -410,6 +410,7 @@ repo-root
 report-dir
 report-prefix
 required-contexts
+require-kubeconfig
 resolv-conf
 resource-container
 resource-quota-sync-period