Master: Update k8s.gcr.io/kube-proxy Docker tag to v1.21.2

This MR contains the following updates:

Package	Type	Update	Change
k8s.gcr.io/kube-proxy	ironbank-docker	minor	v1.19.11 -> v1.21.2
k8s.gcr.io/kube-proxy	stage	minor	v1.19.11 -> v1.21.2

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