Add CI for images/kube-webhook-certgen (#7717)

As a follow up to PR #7641, this commit adds some basic e2e tests for
kube-webhook-certgen image.

Signed-off-by: Mateusz Gozdek <mgozdek@microsoft.com>

images/kube-webhook-certgen/hack/e2e.sh

@@ -0,0 +1,62 @@
+#!/bin/bash
+
+# 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.
+
+if [ -n "$DEBUG" ]; then
+  set -x
+fi
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+pushd rootfs
+go build
+popd
+
+export KUBECONFIG=${KUBECONFIG:-~/.kube/config}
+
+function error {
+  trap - EXIT
+  echo $@
+  exit 1
+}
+
+function cleanup {
+  kubectl delete --recursive -f hack/e2e.yaml --ignore-not-found
+}
+
+trap cleanup EXIT
+
+cleanup
+
+kubectl apply --recursive -f hack/e2e.yaml
+
+./rootfs/kube-webhook-certgen create --kubeconfig ${KUBECONFIG} --namespace test --secret-name test --host test --cert-name test
+./rootfs/kube-webhook-certgen patch --kubeconfig ${KUBECONFIG} --namespace test --secret-name test --webhook-name pod-policy.example.com
+./rootfs/kube-webhook-certgen patch --kubeconfig ${KUBECONFIG} --namespace test --secret-name test --apiservice-name v1alpha1.pod-policy.example.com
+./rootfs/kube-webhook-certgen patch --kubeconfig ${KUBECONFIG} --namespace test --secret-name test --webhook-name pod-policy.example.com --apiservice-name v1alpha1.pod-policy.example.com
+
+if [[ -z "$(kubectl get validatingwebhookconfiguration pod-policy.example.com -o jsonpath='{.webhooks[0].clientConfig.caBundle}')" ]]; then
+  error "ValidatingWebhookConfiguration pod-policy.example.com did not get CA injected"
+fi
+
+if [[ -z "$(kubectl get mutatingwebhookconfiguration pod-policy.example.com -o jsonpath='{.webhooks[0].clientConfig.caBundle}')" ]]; then
+  error "MutatingWebhookConfiguration pod-policy.example.com did not get CA injected"
+fi
+
+if [[ -z "$(kubectl get apiservice v1alpha1.pod-policy.example.com -o jsonpath='{.spec.caBundle}')" ]];then
+  error "APIService v1alpha1.pod-policy.example.com did not get CA injected"
+fi