[Feature Request]: Create User Management Endpoints in API

### Is there an existing feature request for this? - [x] I have searched the existing issues ### What is your feature request? One of our Cronicle instances is used as a managing tool the whole IT-department needs access to. I'd like to sync the users from an existing database so I don't have to create them twice. So I need two API endpoints, for example: - get_user -> to retrieve if it already exists - create_user -> to create if does not exist Another option would be to combine them and use get / post methods to retrieve info or create it. ### Code of Conduct - [x] I agree to follow this project's Code of Conduct