Add tests for Empire functionality

The task is to add a guide and update integration tests to test Empire functionality from https://gitlab.ics.muni.cz/beast-public/cryton-fork/cryton-worker/-/issues/8, https://gitlab.ics.muni.cz/beast-public/cryton-fork/cryton-worker/-/issues/7, https://gitlab.ics.muni.cz/beast-public/cryton-fork/cryton-core/-/issues/19, and https://gitlab.ics.muni.cz/beast-public/cryton-fork/cryton-core/-/issues/20.