Updating Dockerfile.openshift baseimages to mach ocp-build-data config

This PR is autogenerated by the [ocp-build-data-enforcer][1].
It updates the baseimages in the Dockerfile used for promotion in order to ensure it
matches the configuration in the [ocp-build-data repository][2] used
for producing release artifacts.

If you believe the content of this PR is incorrect, please contact the dptp team in
#forum-testplatform.

[1]: https://github.com/openshift/ci-tools/tree/master/cmd/ocp-build-data-enforcer
[2]: https://github.com/openshift/ocp-build-data/tree/openshift-4.6-rhel-8/images

Dockerfile.openshift

@@ -1,8 +1,8 @@
-FROM registry.svc.ci.openshift.org/openshift/release:golang-1.13 AS builder
+FROM registry.svc.ci.openshift.org/ocp/builder:rhel-8-golang-openshift-4.6 AS builder
 WORKDIR /go/src/github.com/kubernetes-csi/external-resizer
 COPY . .
 RUN make build
 
-FROM registry.svc.ci.openshift.org/openshift/origin-v4.0:base
+FROM registry.svc.ci.openshift.org/ocp/4.6:base
 COPY --from=builder /go/src/github.com/kubernetes-csi/external-resizer/bin/csi-resizer /usr/bin/
 ENTRYPOINT ["/usr/bin/csi-resizer"]