Add relationship between countrySubdivision and identical country

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (ec70811) to head (e6b6f32).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #237 +/- ## =========================================== Coverage 100.00% 100.00% - Complexity 268 274 +6 =========================================== Files 42 43 +1 Lines 9633 9641 +8 =========================================== + Hits 9633 9641 +8 ```

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