sre: fix container/pod security context for rsync task
The current sre's security contextes for the rsync task lead to some validation errors from the kube api. I didn't see those before, but this is the first time that I test the dag with k8s 1.31 so things may have become more strict.
Instead of fixing only the sre use case, expand the kubernetes_utils module as well.
Bug: T402512