Bump webpack-dev-server from 3.11.2 to 4.0.0 in /web/app (#6703)

* Bump webpack-dev-server from 3.11.2 to 4.0.0 in /web/app

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 3.11.2 to 4.0.0.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](https://github.com/webpack/webpack-dev-server/compare/v3.11.2...v4.0.0)

---
updated-dependencies:
- dependency-name: webpack-dev-server
  dependency-type: direct:development
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* Move writeToDisk config according to webpack-dev-server v4 migration guide

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Alejandro Pedraza <alejandro@buoyant.io>

web/app/package.json

@@ -81,7 +81,7 @@
     "webpack": "^5.51.1",
     "webpack-bundle-analyzer": "4.4.2",
     "webpack-cli": "4.8.0",
-    "webpack-dev-server": "3.11.2"
+    "webpack-dev-server": "4.0.0"
   },
   "resolutions": {
     "@lingui/**/**/minimist": ">=1.2.5",

web/app/webpack.config.js

@@ -13,7 +13,9 @@ module.exports = {
   mode: process.env.NODE_ENV === 'production' ? 'production' : 'development',
   entry: './js/index.js',
   devServer: {
-    writeToDisk: true
+    devMiddleware: {
+      writeToDisk: true
+    }
   },
   output: {
     path: path.resolve(__dirname, 'dist'),