test images: Adds windows-nanoserver image

This image is the same as "gcr.io/authenticated-image-pulling/windows-nanoserver:v1"
that is used for the "should be able to pull from private registry with secret"
test on Windows.

Adding this image will allow other people to build and push their own
images to their own private registries.

test/images/windows-nanoserver/BASEIMAGE

@@ -0,0 +1,5 @@
+windows/amd64/1809=mcr.microsoft.com/windows/nanoserver:1809
+windows/amd64/1903=mcr.microsoft.com/windows/nanoserver:1903
+windows/amd64/1909=mcr.microsoft.com/windows/nanoserver:1909
+windows/amd64/2004=mcr.microsoft.com/windows/nanoserver:2004
+windows/amd64/20H2=mcr.microsoft.com/windows/nanoserver:20H2

test/images/windows-nanoserver/Dockerfile

@@ -0,0 +1,19 @@
+# Copyright 2021 The Kubernetes Authors.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# NOTE(claudiub): Noop. We're just mirroring the image to staging.
+ARG BASEIMAGE
+FROM $BASEIMAGE
+
+LABEL image_version="v1"

test/images/windows-nanoserver/VERSION

@@ -0,0 +1 @@
+v1