etcdadm: create job to push builds to staging

config/jobs/image-pushing/k8s-staging-etcdadm.yaml

@@ -0,0 +1,27 @@
+postsubmits:
+  kubernetes-sigs/etcdadm:
+    - name: etcdadm-postsubmit-push-to-staging
+      cluster: k8s-infra-prow-build-trusted
+      annotations:
+        testgrid-dashboards: sig-cluster-lifecycle-etcdadm
+      decorate: true
+      branches:
+        - ^master$
+        - ^release-.*
+        # Build tags also
+        # this is a regex for semver, from https://semver.org/#is-there-a-suggested-regular-expression-regex-to-check-a-semver-string
+        - ^v(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-((?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\.(?:0|[1-9]\d*|\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\+([0-9a-zA-Z-]+(?:\.[0-9a-zA-Z-]+)*))?$
+      spec:
+        serviceAccountName: gcb-builder
+        containers:
+          - image: gcr.io/k8s-testimages/image-builder:v20200901-ab141a0
+            command:
+              - /run.sh
+            args:
+              # this is the project GCB will run in, which is the same as the GCR images are pushed to.
+              - --project=k8s-staging-etcdadm
+              - --scratch-bucket=gs://k8s-staging-etcdadm-gcb
+              - --env-passthrough=PULL_BASE_REF
+              - --with-git-dir
+              - --build-dir=.
+              - dev/staging/