[stable32] feat: Save a checksum for documents and use it to detect conflicts

[backportbot]

Backport of PR #7677

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 52.80%. Comparing base (d64ed4f) to head (295c61f).
⚠️ Report is 7 commits behind head on stable32.

Additional details and impacted files

@@             Coverage Diff              @@
##           stable32    #7725      +/-   ##
============================================
+ Coverage     52.66%   52.80%   +0.13%     
============================================
  Files           503      503              
  Lines         44206    44106     -100     
  Branches       1129     1128       -1     
============================================
+ Hits          23281    23288       +7     
+ Misses        20816    20715     -101     
+ Partials        109      103       -6     

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