Add tests for user_group_distinguished_names()

In https://github.com/stackabletech/opa-operator/pull/622#top we added an Active Directory backend to the user info fetcher.

As part of this, there was fairly extensive code to convert between some weird representations which AD chose for userids and groupids.

In order to not block the release with this we decided to punt on adding unit tests (hopefully, worst case: integration tests) for this later.

We should try and get this done fairly soon after 24.11.

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pull request 622 で追加された実装および変換コード、特に user_group_distinguished_names() のパスから始めてください。Active Directory のユーザー ID とグループ ID の表現を対象とする単体テスト、または必要に応じて統合テストを追加してください。完了とは、リリースをブロックせずに変換動作がテストされていることを意味します。