build(deps-dev): bump webpack-merge from 5.4.0 to 5.7.3 in /frontend

Bumps [webpack-merge](https://github.com/survivejs/webpack-merge) from 5.4.0 to 5.7.3.
- [Release notes](https://github.com/survivejs/webpack-merge/releases)
- [Changelog](https://github.com/survivejs/webpack-merge/blob/develop/CHANGELOG.md)
- [Commits](survivejs/webpack-merge@v5.4.0...v5.7.3)

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

Author: dependabot[bot]

frontend/package-lock.json

@@ -48,7 +48,7 @@
     "webpack": "^4.40.2",
     "webpack-cli": "^4.0.0",
     "webpack-dev-server": "^3.11.2",
-    "webpack-merge": "^5.2.0"
+    "webpack-merge": "^5.7.3"
   },
   "dependencies": {
     "chartist": "^0.11.3",