Cleanup archived workers and models

arkindex/documents/management/commands/cleanup.py

arkindex/documents/tests/commands/test_cleanup.py

arkindex/process/managers.py

arkindex/project/config.py

arkindex/project/settings.py

arkindex/project/tests/config_samples/defaults.yaml

arkindex/project/tests/config_samples/errors.yaml

arkindex/project/tests/config_samples/expected_errors.yaml

arkindex/project/tests/config_samples/override.yaml