Add clean target in Makefile

[runzhen]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

The "make" command generated 4 binaries, but we need to delete these files manually.
Add a "clean" target in Makefile, so that user can run "make clean" to cleanup these binaries.

Which issue(s) this PR is related to:

Special notes for your reviewer:

Does this PR introduce a user-facing change?

Additional documentation (design docs, usage docs, etc.):

Checklist

• make check test passes locally
• make check-generate passes if api/ changed (CRDs, deepcopy, informers, listers, clientset)
• make check-modules passes if go.mod / go.sum changed
• Tests added or updated for the change
• Helm chart (deployments/helm) updated if flags, RBAC, or defaults changed

[k8s-ci-robot]

Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: runzhen
Once this PR has been reviewed and has the lgtm label, please assign klueska for approval. For more information see the Code Review Process.

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[k8s-ci-robot]

Hi @runzhen. 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.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.