pause image is still on RHEL 8

Recently we bumped the hyperkube image [1] to use both RHEL 9 builder and base images.

In order to keep things consistent, we tried to do the same with the "pause" image [2], however, that caused mass failures in payload jobs [3] due to a mismatch with ART [4], which still builds that image with RHEL 8.

As a result, we decided to keep builder & base images for "pause" in RHEL 8, as this work was not required for the kube 1.28 bump nor the FIPS issue we were addressing.

However, for the sake of consistency, eventually it'd be good to bump the "pause" builder & base images to RHEL 9.

[1] https://github.com/openshift/kubernetes/blob/6ab54b8d9a0ea02856efd3835b6f9df5da9ce115/openshift-hack/images/hyperkube/Dockerfile.rhel#L1

[2] https://github.com/openshift/kubernetes/blob/6ab54b8d9a0ea02856efd3835b6f9df5da9ce115/build/pause/Dockerfile.Rhel#L1

[3] https://github.com/openshift/kubernetes/blob/6ab54b8d9a0ea02856efd3835b6f9df5da9ce115/build/pause/Dockerfile.Rhel#L1

[4] https://github.com/openshift-eng/ocp-build-data/blob/openshift-4.15/images/openshift-enterprise-pod.yml

4.15

Always

1.
2.
3.

Builder & base images for "pause" are RHEL 8.

Builder & base images for "pause" are RHEL 9.