Automatic merge from submit-queue (batch tested with PRs 63598, 63913, 63459, 63963, 60464). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Client-go raises error on duplicated name in kubeconfig

(for NamedCluster, NamedContext, NamedUser, NamedExtension)



**What this PR does / why we need it**:
Client should detect duplicated name when loading `name-value` based lists in kubeconfig: `users`, `clusters`, `contexts`. Currently if there are multiple value with same name, `client-python` will pick the first one, while `client-go` will pick the last.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
ref: kubernetes-client/python#445, kubernetes-client/python-base#47

**Special notes for your reviewer**:

**Release note**:

```release-note
kubectl and client-go now detects duplicated name for user, cluster and context when loading kubeconfig and reports error 
```

/sig api-machinery

cc @brendandburns @mbohlool