Install the Python libs to system site-packages instead of root

[oysstu]

🦟 Bug fix

Fixes #2206

Summary

Changes are copied from gz-math

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (8f84b05) 65.62% compared to head (71e77b4) 65.61%.

Additional details and impacted files

@@             Coverage Diff             @@
##           gz-sim8    #2274      +/-   ##
===========================================
- Coverage    65.62%   65.61%   -0.01%     
===========================================
  Files          324      324              
  Lines        30925    30925              
===========================================
- Hits         20293    20292       -1     
- Misses       10632    10633       +1     

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[azeey]

LGTM! We should be able to simplify the whole logic for Ionic since we're using a newer version of CMake.