docs: Warn about non-deterministic lazy row indexes

[Whning0513]

Fixes #28294.

Warn that adding a row index to a non-deterministic LazyFrame can make the index relationship to other columns unpredictable.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.36%. Comparing base (36e414b) to head (f73d1af).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #28622      +/-   ##
==========================================
- Coverage   81.71%   81.36%   -0.36%     
==========================================
  Files        1870     1870              
  Lines      262992   262972      -20     
  Branches     3217     3217              
==========================================
- Hits       214917   213977     -940     
- Misses      47243    48163     +920     
  Partials      832      832              

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