add support for watch APIs

[tanmaykm]

This adds support for watch APIs.

Kubernetes provides efficient change notifications on resources via "watches". Certain entities have the special watch APIs defined for them and that can be invoked with the watch verb. The watch API accepts a Channel through which it streams events.

watch(ctx::KuberContext, T::Symbol, outstream::Channel, args...; kwargs...)

In addition, verbs like get and list also support watches, and those can be invoked as:

watch(ctx, verb, args...; kwargs...) do stream
    for event in stream
        # process event
    end
end

E.g.:

watch(ctx, list, :Pod; resourceVersion=19451) do stream
    for event in stream
        @info("got event", event)
    end
end