Support for containerd

[ryanwr]

Hi,

Thanks for this tool!

Would be good if you could also support containerd. I have a small k3s cluster and would like to see the container stats to show up along with the server stats.

It looks like containerd only supports gRPC over the unix socket: https://dnephin.github.io/containerd/github.com/containerd/containerd/api/services/containers/v1/containers.html

[henrygd]

I'll look into it at some point, but I don't think that API provides resource usage, so we'd probably need to use cgroups directly.