Update kube-rbac-proxy to v0.8.0

[hidekazuna]

/kind feature

Describe the solution you'd like

Current kube-rbac-proxy version is v0.4.1. But It seems better to update kube-rbac-proxy to v0.8.0.

Anything else you would like to add:

Cluster API uses v0.8.0.
https://github.com/kubernetes-sigs/cluster-api/blob/master/config/manager/manager_auth_proxy_patch.yaml

[hidekazuna]

This will be done when upgrading to v1alpha4:
https://github.com/kubernetes-sigs/cluster-api/blob/master/docs/book/src/developer/providers/v1alpha3-to-v1alpha4.md#upgrade-kube-rbac-proxy-to-v080

[jichenjc]

@hidekazuna I think we can close this as we have a v1alpha4 PR already

[hidekazuna]

@jichenjc I will close this issue if #748 is merged.