Add Betreuungskosten pointer to synthetic data.

[MImmesberger]

When creating synthetic data, the input variable p_id_betreuungsk_träger is currently set to 0 for everyone. I adjusted this to be the same as p_id_kindergeld_empf.

[codecov[bot]]

Codecov Report

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

Project coverage is 89.62%. Comparing base (95f11ff) to head (b601ea9). Report is 8 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #769 +/- ## ======================================= Coverage 89.62% 89.62% ======================================= Files 52 52 Lines 3767 3768 +1 ======================================= + Hits 3376 3377 +1 Misses 391 391 ```

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