[Idea] Add "init" subcommand to CLI

[ericcornelissen]

This issue is just to share an idea for a feature for the WebMangler CLI: add a subcommand (or option) called "init" to initialize a WebMangler setup for a project. The bare minimum would be adding the WebMangler Core and the WebMangler CLI as a dependency and adding some template configuration file.

If anyone has ideas for other things that could be part of the "init" subcommand, feel free to share them here.

See also https://docs.npmjs.com/cli/v8/commands/npm-init