Add support for feature toggles

Feature toggles enable the capacity to roll-out different features to a certain group of users based on different criteria (more info here https://martinfowler.com/articles/feature-toggles.html)

We need to integrate a tool that can help us to release features using flags. It seems https://bullet-train.io/ is a nice tool that can be evaluated for free (20000 requests for free) so we need to check if there are other options or just using this one.

**Acceptance Criteria**
- A feature flags tool is integrated with the project
- README file is updated with the basic info about how to manage toggles in the app
- Share with the team the mechanism that is going to be used to release new features to certain users/tenants