Allow configuring the webpackHotDevClient with a url

Created by: rzane

This allows configuring the webpackHotClient with a URL. Currently, the hot client assumes that your frontend code is served from the same window.location, but this is often not true for server-rendered applications using the webpack-dev-server.

This can be configured like so:

entry: [
  `${require.resolve('react-dev-utils/webpackHotDevClient')}?http://0.0.0.0:4001`,
  'your-entry.js'
]

See: https://github.com/webpack/webpack-dev-server/blob/544d97bf4bee3853c84abb8690923bf93fda4fab/client/index.js#L22