fix(ske): retain audit and labels fields in generate-payload output

[MichaelEischer]

Description

The stackit ske cluster generate-payload --cluster-name ... command can be used to retrieve the cluster description that can be used to create or update a cluster. A few recent SDK updates, have added new toplevel fields that were missing such that a generate-payload and update roundtrip could loose configuration options.

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see e.g. here)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)