upgrade client-go version to 0.21.2

[johnlanni]

Upgrade sigs.k8s.io/controller-runtime from 0.6.0 to 0.9.2, because 0.6.0 is too old to be compatible with many pkgs.
Upgrade k8s.io/client-go from 0.18.3 to 0.21.2, because controller-runtime 0.9.2 needs.

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[johnlanni]

@googlebot I signed it