Deprecate the rbac-proxy in stunner-gateway-operator

[rg0now]

We no longer deploy the kube-rbac-proxy: it was never really needed to begin with, plus it's now deprecated (see l7mp/stunner#185). The operator kustomize pipeline has been changed so that we no longer deploy the rbac-proxy (see l7mp/stunner-gateway-operator@79212a8). This change needs to be carried over here.

The major difference is that we have disabled the manager_auth_proxy_patch.yaml kustomize patch. This effectively removes the kube-rbac-proxy sidecar container in the controller-manager Deployment. The simplest way to see the effects is to run kustomize build config/default in the stunner-gateway-operator repo and compare the output with the Helm templates.