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-artifacts.sh

@@ -0,0 +1,55 @@
+# 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.
+
+# injects new image/tag into the images in ./release/kubernetes-manifests/demo.yaml 
+
+#!/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}"
+
+# overwrite release/ with the latest manifests, adding "---" separator.
+src="./kubernetes-manifests/*"
+manifestfile="./release/kubernetes-manifests/demo.yaml"
+tmp="./release/kubernetes-manifests/tmp.yaml"
+[ -e $manifestfile ] && rm $manifestfile
+for f in $src; do (cat "${f}"; echo "---") >> $tmp; done
+
+# remove extra google headers 
+gsed -i '/^#/d' $tmp 
+
+# remove empty lines 
+gsed -r -i '/^\s*$/d' $tmp 
+
+# add 1 google header to the top 
+cat "./release/.googleheader" $tmp > $manifestfile 
+rm $tmp 
+
+
+# replace image repo, tag for each deployment  
+for dir in ./src/*/    
+do
+    svcname="$(basename $dir)"
+    image="$REPO_PREFIX/$svcname:$TAG"
+
+    pattern="^(\s*)image:\s.*$svcname(.*)(\s*)"
+    replace="\1image: $image\3"  
+    gsed -r -i "s|$pattern|$replace|g" $manifestfile
+done
+
+log "Successfully added image tags > wrote to demo.yaml".