added documentation for custom transformation in reverse replication

[shreyakhajanchi]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 54.26%. Comparing base (569a68c) to head (354a67f).
Report is 13 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2097      +/-   ##
============================================
+ Coverage     46.39%   54.26%   +7.86%     
+ Complexity     3931     1553    -2378     
============================================
  Files           859      396     -463     
  Lines         51300    21460   -29840     
  Branches       5394     2145    -3249     
============================================
- Hits          23803    11646   -12157     
+ Misses        25783     9122   -16661     
+ Partials       1714      692    -1022     

Components	Coverage Δ
spanner-templates	69.65% <ø> (+1.39%)	⬆️
spanner-import-export	∅ <ø> (∅)
spanner-live-forward-migration	76.67% <ø> (ø)
spanner-live-reverse-replication	77.93% <ø> (ø)
spanner-bulk-migration	87.39% <ø> (+0.08%)	⬆️

see 492 files with indirect coverage changes