Add `package-mode` option to `init` and `new` commands

[rHuggler]

Pull Request Check List

Resolves: #discussion-6739305

• [x] Added tests for changed code.
• [x] Updated documentation for changed code.

---

This PR adds a --package-mode option (defaults to "true") to both init and new commands. When false is passed, the project will be initialised in non-package mode.

[dimbleby]

Per the linked discussion, I'd expect that when in non-package mode initialisation would skip the README - and also the version, and all the other fields that are not needed in non-package mode.

[rHuggler]

I'll work on it