Use new SLI metric instead of soon to be deprecated SLO metrics in 1.26

In Kubernetes 1.26 we renamed the apiserver_request_slo_duration_seconds metric to apiserver_request_sli_duration_seconds: https://github.com/kubernetes/kubernetes/pull/112679 and we are looking at removing the slo metric in 1.27. As such, the mixins should be updated to use the new metric.