Create new Backend Group - Model for Users

Backend API on Swagger: [https://staging.fightpandemics.work/api/documentation/index.html#/default](https://staging.fightpandemics.work/api/documentation/index.html#/default)

Create new Group Backend (please review MVVM architecture - if you have any questions, please reach out to Scott (@Power186)

Start with the Swagger API documentation linked in the issue, then review the repository's MVVM architecture and existing backend groups or models. Confirm the Users model's API shape and how it should fit the architecture; done means the new Users backend group/model is represented consistently with the API.

Written by the indexing model from the issue text.