Add Helm chart to ease deployment on Kubernetes

[andras-kth]

Standard fare Helm chart with formats as the only binfmt-specific configuration option
and a subset of standard options that allow Kubernetes administrators to select a subset
of nodes for installation.

[tonistiigi]

@morlay @AkihiroSuda

[AkihiroSuda]

Can we test this on CI? (With kind/minikube, or k3s)

[andras-kth]

Actually, I've just realized that this is already partially handled by the Kubernetes driver's qemu.install option.
https://github.com/docker/buildx/blob/610601cec0d9c0a5a93e67a0054b3f2243a61273/driver/kubernetes/factory.go#L136

I suppose if that got changed from a bool to a string option that specified the relevant formats,
that would be a much better approach, especially considering that this PR's Helm chart doesn't
work so well with auto-scaled clusters where nodes may come and go...