Bump webpack-dev-server from 3.11.2 to 4.6.0 in /ui

Bumps [webpack-dev-server](https://github.com/webpack/webpack-dev-server) from 3.11.2 to 4.6.0.
- [Release notes](https://github.com/webpack/webpack-dev-server/releases)
- [Changelog](https://github.com/webpack/webpack-dev-server/blob/master/CHANGELOG.md)
- [Commits](webpack/webpack-dev-server@v3.11.2...v4.6.0)

---
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>

ui/package.json

@@ -88,7 +88,7 @@
     "webpack": "^4.46.0",
     "webpack-bundle-analyzer": "^4.4.2",
     "webpack-cli": "^3.3.6",
-    "webpack-dev-server": "^3.11.2",
+    "webpack-dev-server": "^4.6.0",
     "webpack-merge": "^4.2.1"
   },
   "engines": {