Update webpack to latest supported version

[vincentfretin]

Description:

Update build tools dependencies.

Changes proposed:

• Update webpack and associated loaders
• Update webpack-dev-server, this requires now at least node 18.12.0 that everyone should have, older versions of node aren't supported anymore. Current LTS is node 20.x
• Remove webpack-merge dependency, webpack now supports extending another configuration with "extends"

[dmarcos]

Are any of these updates needed? In general I avoid updating dependencies unless there's a reason to do so. If things work no reason to get exposed to API changes, regressions, new bugs

[vincentfretin]

Not currently needed per se, just maintenance, so we don't need to check the changelog of 30 versions of those dependencies in 5 years when we really need to upgrade because of a blocker like we had with budo and self-signed certificate not working on ubuntu 22.04.

Please be aware that we don't push package-lock.json in the repo, so we effectively auto upgrade all those dependencies when you freshly git clone the repo and run npm install.
Here are the only real upgrades:

• "webpack-cli" from "4.x.x" to 5.x.x"
• "webpack-dev-server" from "4.x.x" to "5.x.x"
• "babel-loader" from "8.x.x" to "9.x.x"

that removes support for node 16.x. That's the only api changes as far as I'm aware after reading the changelogs. The dist didn't change after those upgrades.
And this also remove webpack-merge dependency, that's always nice to remove dependencies.

Feel free to leave it open until we really need it. I'll just update it the next time I read the changelogs in a year :D