cmd/k8s-operator,k8s-operator,go.{mod,sum}: make individual proxy images/image pull policies configurable
Allow to configure images and image pull policies for individual proxies
via ProxyClass.Spec.StatefulSet.Pod.{TailscaleContainer,TailscaleInitContainer}.Image,
and ProxyClass.Spec.StatefulSet.Pod.{TailscaleContainer,TailscaleInitContainer}.ImagePullPolicy
fields.
Document that we have images in ghcr.io on the relevant Helm chart fields.
Updates tailscale/tailscale#11675
Signed-off-by: Irbe Krumina <irbe@tailscale.com>