Implement mechanism for deactivating users

[VKTB]

Description

This PR modifies the logic for refreshing the access token so that the username in its payload is checked to see if it is part of the active usernames list before it refreshes it.

Testing instructions

Add a set of instructions describing how the reviewer should test the code

• Review code
• Check Actions build

Agile board tracking

closes #12

[VKTB]

I made some changes so that the env var values used during testing are overridden using pytest.ini instead of using the pytest_configure hook. As such, the tests should now be run with the following command: pytest -c test/pytest.ini test. README was updated accordingly. Please also run pip install .[dev] as pyproject.toml has been updated.