[DE] Add `osu!_tournament_client` and `Tournament_management_commands`

[The-Last-Cookie]

This is part of a series that aims to add all articles under osu!_tournament_client.

Translation notes:

• scene > Kulisse
• round editor > Runden-Editor
• seeding results editor > Editor für Platzierungsergebnisse

Self-check

• [x] The changes are tested against the contribution checklist
• [ ] (translations only) The changes are reviewed on GitHub by a fluent speaker