build(deps-dev): bump css-minimizer-webpack-plugin in /frontend (#894)

Bumps [css-minimizer-webpack-plugin](https://github.com/webpack-contrib/css-minimizer-webpack-plugin) from 1.2.0 to 2.0.0.
- [Release notes](https://github.com/webpack-contrib/css-minimizer-webpack-plugin/releases)
- [Changelog](https://github.com/webpack-contrib/css-minimizer-webpack-plugin/blob/master/CHANGELOG.md)
- [Commits](webpack/css-minimizer-webpack-plugin@v1.2.0...v2.0.0)

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Author: dependabot[bot]