add create system user

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.66667% with 4 lines in your changes missing coverage. Please review.

Project coverage is 57.14%. Comparing base (7e7cf1f) to head (36d6813). Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
src/jupyterhub_config/custom_spawner.py	86.66%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #79 +/- ## ========================================== + Coverage 49.60% 57.14% +7.54% ========================================== Files 5 5 Lines 125 154 +29 ========================================== + Hits 62 88 +26 - Misses 63 66 +3 ```

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