Add a simple Procfile to serve static assets (#155)

* Sets a Procfile to use a Ruby HTTP server to serve up the app as a static site.
* Adds a heroku-postbuild script in package.json which builds both the app and the web component. This takes precedence over build in the Heroku build process. This has a special env var of PUBLIC_URL set to an empty string so the webcomponent builds properly.
* Adds a .dockerignore to make the docker build context smaller for faster local container rebuilds
* Adds an app.json just to make the Heroku deployment a bit more in-keeping with other apps.

Author: patch0

.dockerignore

@@ -0,0 +1,4 @@
+build/
+dist/
+.git/
+node_modules/

Procfile

@@ -0,0 +1 @@
+web: ruby -run -e httpd -- -p $PORT build/

README.md

@@ -55,3 +55,6 @@ Open [http://localhost:3001](http://localhost:3001) to view it in the browser.
 
 There is no production build setup for the web component at present.
 
+## Review apps
+
+Currently the build is deployed to both S3 and Heroku.  The PR should get updated with the Heroku URL, and the web component demo is at `/web-component.html` on the Heroku review app domain.

app.json

@@ -0,0 +1,13 @@
+{
+  "name": "editor-ui",
+  "formation": {
+    "web": {
+      "quantity": 1
+    }
+  },
+  "buildpacks": [
+    {
+      "url": "heroku/nodejs"
+    }
+  ]
+}

package.json

@@ -57,7 +57,8 @@
     "test": "node scripts/test.js --transformIgnorePatterns 'node_modules/(?!three)/'",
     "test:integration": "cd e2e; docker compose up --exit-code-from cypress",
     "start:wc": "NODE_ENV=development BABEL_ENV=development webpack serve -c ./webpack.component.config.js",
-    "build:wc": "NODE_ENV=production BABEL_ENV=production webpack build -c ./webpack.component.config.js"
+    "build:wc": "NODE_ENV=production BABEL_ENV=production webpack build -c ./webpack.component.config.js",
+    "heroku-postbuild": "export PUBLIC_URL='' && yarn build && yarn build:wc"
   },
   "eslintConfig": {
     "extends": [