Improve the demo app

[pBouillon]

Issue Summary

The documentation is great, but it could be better to showcase a real use case of the library using a backend and an Angular frontend relying on ngx-flagr.

This could help users to get started by digging into a practical use case.

The example must be as accessible (from a develop point of view) as possible so the backend should not be the main focus. However, to match Angular's user tech stack, it might be better to use either .NET (which also happens to have built-in feature flags management), or a simpler Node server.

Category

- [ ] Bug report
- [ ] Regression
- [ ] Feature suggestion
- [ ] Documentation issue
- [x] Other

Expected Behavior

N/A

Actual Behavior

The demo app is still only a simple Angular app consisting of a single page and not much practical logic or real life use case

Steps to Reproduce

N/A

Environment

N/A

Additional Information

• The example should include its own README on how to set it up, ideally with a docker container and possibly a .devcontainer

I am not sure what the best way to showcase the library could be, I am open to suggestions for that - before any coding, ideally (simple feature toggle use case, A/B testing, something else, all of those but in separate projects/routes?)