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.

Issue checklist

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• Describe the use-case, as far is possible. For instance, using the pattern "As a XXXX, I would like XXXX to be able to do XXXX" helps to identify the feature as well as the problem it is intended to address.
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• Indicate if there is a known work-around until such time as the issue has been implemented.

Inizia dal codice di implementazione e conversione aggiunto in pull request 622, in particolare dal percorso user_group_distinguished_names(). Aggiungi unit test o, se necessario, test di integrazione che coprano le rappresentazioni degli ID utente e gruppo di Active Directory; il lavoro è completato quando il comportamento di conversione è verificato senza bloccare il release.