Serve-index v2

[bjohansebas]

Okay, I need this so that webpack-dev-server can be migrated to Express 5, in order to avoid issues with the Content-Type. Basically, what I want to do in this new version is:

• Drop support for old Node.js versions (Node <18) (blocke by Fix Node.js 18+ support #117)
• Update dependencies to their major versions

[bjohansebas]

Okay, with #152 and #151 the dependencies will be deduplicated, and now webpack-dev-server will have the same MIME types for all files.