teal Addin - allow users to pick modules, based on which default app templates and project structure will be created

Please see details on the linked draft proposal below

[Draft proposal](https://docs.google.com/document/d/1Zib6ZzOaANPdRsQ_t6kNfSYMo0U5UGcdsx95N92NoCw/edit)

Issues:
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/58
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/59
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/51
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/66
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/67
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/53
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/52
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/54
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/55
- [ ] https://github.com/insightsengineering/NEST-roadmap/issues/56

Later we can improve:
- arguments customization
- data customization

Note: Be aware that app.R might grow too big, consider splitting into several files sourced in app.R (data.R, args.R, etc.)