fix: add namespace autocompletion for kubectl config set-context command

[TessaIO]

What type of PR is this?

/kind feature

What this PR does / why we need it:

This PR aims to add the namespace autocompletion for kubectl config set-context command

Which issue(s) this PR fixes:

Fixes kubernetes/kubectl#1564

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Added namespace autocompletion for kubectl config set-context command

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

N/A

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[TessaIO]

@ah8ad3 wanna take a look at this?

[dharmit]

I can confirm that it works as expected:

$ _output/bin/kubectl config set-context --current --namespace
-- completions --
default          kube-node-lease  kube-public      kube-system

[ardaguclu]

I think, simplified version would be like in here

kubernetes/staging/src/k8s.io/kubectl/pkg/cmd/top/top_pod.go

Line 104 in 00c3094

ValidArgsFunction: completion.ResourceNameCompletionFunc(f, "pod"),

;

ValidArgsFunction:     completion.ResourceNameCompletionFunc(f, "namespace"),

WDYT?

[TessaIO]

We're actually setting:

ValidArgsFunction: completion.ContextCompletionFunc

We can't override it right?

[ah8ad3]

I don't think that's possible to replace these two, because the added behavior only runs completion for namespace flag. But i think it's more cleaner IMO to move this section inside ContextCompletionFunc, this looks good too.

[k8s-ci-robot]

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[TessaIO]

@ardaguclu thanks for the review! I updated the code and left some replies.

[TessaIO]

/retest