Code initial cmd-admission-webhook-k8s

[edwarnicke]

Write an admissions webhook similar to https://github.com/networkservicemesh/networkservicemesh/tree/master/k8s/cmd/admission-webhook

Please do not bring across the "github.com/networkservicemesh/networkservicemesh/*" dependencies. Many of them do not need to be replicated (like probes). Keep things simple :)

@Bolodya1997 do we need to update the NSM URL schema compared to https://github.com/networkservicemesh/networkservicemesh/blob/756a5e48592b29174765657cf3a4cb79c3491240/pkg/tools/tools.go#L195 ? Do we have a lib in sdk for that currently? I recall you did some smart things for sriov in terms of updating the URL.. but don't remember them precisely. Pointers welcome :)