RHCOS 9 Support

4.13 is going to be based on RHCOS 9, which is a major OS version bump. We've already found some potential issues with that because we deal with a lot of host networking that has hard dependencies on the underlying OS. Here is a (likely incomplete) list of potential issues we know of today:

• We call the host oc binary in one of our init containers. This can break if the container image version doesn't match the host OS version. Bug report from early RHEL 9 testing
• We use the host iptables from (I think) the haproxy monitor container. This may also have issues if the version doesn't match.
• NMState is considering moving to the Rust implementation in 9.0. While initial testing has been positive, there is a high probability that this has some impacts on kubernetes-nmstate.

The possibility exists that none of this ends up being a real problem, but the possibility also exists that there are problems we don't even know about yet. I think it's important to keep this in mind as we plan for 4.13.