Adds make-release script, static k8s manifests (#132)

Closes #75.  

### Changelog 

Adds 4 scripts to the `hack/` directory for building/pushing images, injecting images tags into static manifests, and tagging new releases. See [hack/README.md](https://github.com/m-okeefe/microservices-demo/tree/release-script/hack). 

**Note**: since we have not pushed images yet, the images in the `./release/` manifests are still set to the skaffold defaults (eg. `adservice`).

hack/make-release.sh

@@ -0,0 +1,41 @@
+# Copyright 2019 Google LLC
+#
+# 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.
+
+# Creates a new release by 1) building/pushing images, 2) injecting tag into YAML, 
+# 3) creating a new git tag, and 4) pushing tags/updated YAML to $BRANCH.
+
+#!/usr/bin/env bash
+set -euo pipefail
+
+log() { echo "$1" >&2; }
+fail() { log "$1"; exit 1; }
+
+TAG="${TAG?TAG env variable must be specified}"
+REPO_PREFIX="${REPO_PREFIX?REPO_PREFIX env variable must be specified}"
+
+# build and push images 
+./hack/make-docker-images.sh
+
+# update yaml 
+./hack/make-release-artifacts.sh 
+
+# create git release / push to master 
+log "Pushing k8s manifests to master..."
+git tag "$TAG"
+git add release/
+git commit --allow-empty -m "Release $TAG"
+git push --tags
+git push origin master
+
+log "Successfully tagged release $TAG."