Add support for production kedro viz backend (#318)

Allows development using data from a production backend server, by enabling a production sever running through `kedro viz --port 4142` to run alongside the dev server through `npm run start`, while forwarding requests to the production API backend.

Adds a dev server [proxy](https://create-react-app.dev/docs/proxying-api-requests-in-development/) to local production servers on `4142`, which activates only for requests that don't respond on the dev server.

package.json

@@ -6,6 +6,7 @@
     "lib"
   ],
   "homepage": ".",
+  "proxy": "http://localhost:4142/",
   "scripts": {
     "build": "npm run build:css && react-scripts build",
     "build:css": "node-sass src/ -o src/",