Automatic merge from submit-queue

Add a check in ConfirmUsable() to validate the contextName

**What this PR does / why we need it**:
When a context name is provided, but can't be found (miss spelling), it currently
uses the defaults. This PR will cause the command to fail, to prevent unexpected side effects
of using the wrong configuration.

**Which issue this PR fixes**
fixes #21062

**Special notes for your reviewer**:
None

**Release note**:
```release-note
Error if a contextName is provided but not found in the kubeconfig.
```