TypeScript support for setupProxy

Created by: dannycochran

I understand the docs specifically call out that the setupProxy file does not support additional languages. However, without TypeScript support, the setupProxy file cannot import other TypeScript code from within src.

My use case:

// src/setupProxy.js
//
// @ts-ignore: isolated modules error
const proxy = require('http-proxy-middleware');
const backends = require('./common/backends');
const addressInfo = backends.getServerAddress();

module.exports = function (app) {
  app.use(proxy([
    backends.apiRoot,
    backends.graphqlRoot,
    backends.mediaRoot,
  ], { target: `http://${addressInfo.host}:${addressInfo.port}/` }));
};

This will result in an error, Cannot find module './common/backends', which makes sense because ./common/backends is a TypeScript file. However, I would be able to require this file if my project were JavaScript.

Without this, I'll have to duplicate the addressInfo and path locations from backends in setupProxy.