Add RuntimeClass metrics

[tallclair]

We should add RuntimeClass metrics. Maybe as an additional label on kube_pod_info?

/cc @egernst @SergeyKanzhelev

/kind feature

[egernst]

Thanks @tallclair

I think we want something similar to #1053, but for runtimeclass itself.

[lilic]

@egernst @egernst can you please explain the feature request in a bit more details so we can evaluate if we want this added or not, thanks!

[egernst]

@lilic thanks. As a user I would like to verify that a given RuntimeClass handler is being utilized, and how it is behaving from a health perspective.

When combined with kube_pod_status_phase, end-users can use tools like Grafana to quickly assess how pods running with various runtimeclass handlers compare. This is very similar to what was done for PodOverhead: #1053

I would want to add something like a gauge with label key kube_pod_runtimeclass_handler, and label value the handler being used.

[lilic]

Thanks @egernst sounds good to me! Are you interested in contributing this, otherwise we can mark it as help wanted. Note we are in the release 2.0 cycle so might be some delay in getting PRs merged.

[egernst]

Is there a cutoff for 2.0? I saw alpha from earlier this month (thanks!).

In a perfect world, I would contribute this ASAP and it would be available in 2.0. Do you think this is feasible?