for kubelet, when --image-service-endpoint is not set, kubelet would use
the runtime socket as the image-service endpoint.

under kubelet using runtime-manager as remote runtime and image-service not configured scenario :
	kubelet xx --container-runtime-endpoint=/var/run/runtime-manager/runtimemanager.sock
runtime-manager should implement image service proxy, otherwise there would be image related errors
as no image-service exists.

runtime-manager just forwards image request to backend containerd tranparently.
Signed-off-by: honpey <honpey@gmail.com>