Add allowed hosts setting for webpack dev server

GCK needs to allow multiple hosts since it is accessed via Docker
internal networking

config/webpack.config.js

@@ -19,6 +19,8 @@ const IS_EE = require('./helpers/is_ee_env');
 const DEV_SERVER_HOST = process.env.DEV_SERVER_HOST || 'localhost';
 const DEV_SERVER_PORT = parseInt(process.env.DEV_SERVER_PORT, 10) || 3808;
 const DEV_SERVER_PUBLIC_ADDR = process.env.DEV_SERVER_PUBLIC_ADDR;
+const DEV_SERVER_ALLOWED_HOSTS =
+  process.env.DEV_SERVER_ALLOWED_HOSTS && process.env.DEV_SERVER_ALLOWED_HOSTS.split(',');
 const DEV_SERVER_HTTPS = process.env.DEV_SERVER_HTTPS && process.env.DEV_SERVER_HTTPS !== 'false';
 const DEV_SERVER_LIVERELOAD = IS_DEV_SERVER && process.env.DEV_SERVER_LIVERELOAD !== 'false';
 const WEBPACK_REPORT = process.env.WEBPACK_REPORT && process.env.WEBPACK_REPORT !== 'false';
@@ -556,6 +558,7 @@ module.exports = {
     host: DEV_SERVER_HOST,
     port: DEV_SERVER_PORT,
     public: DEV_SERVER_PUBLIC_ADDR,
+    allowedHosts: DEV_SERVER_ALLOWED_HOSTS,
     https: DEV_SERVER_HTTPS,
     contentBase: false,
     stats: 'errors-only',