Add krew auto completion

[zhengtianbao]

What type of PR is this?

/kind feature

What this PR does / why we need it:

Add krew auto completion scripts.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

Add auto completion for krew  addon

[k8s-ci-robot]

Hi @zhengtianbao. Thanks for your PR.

I'm waiting for a kubernetes-sigs member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

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[floryut]

/ok-to-test
I'm not using it but that might be a welcome addition for people using it

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: floryut, zhengtianbao

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[cristicalin]

Nice addon, thanks @zhengtianbao !

/lgtm