[Iceberg CDC source] Allow dropping PK or watermark columns

[ahmedabu98]

Allows dropping primary key columns or watermark column in CDC reads. The source still reads them internally to function properly, then drops them in a final step. Configurations that are valid today keep the same graph and coders, so this is update compatible.

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[ahmedabu98]

assign set of reviewers

[github-actions]

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R: @Abacn for label java.
R: @chamikaramj for label iceberg.

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[ahmedabu98]

Java unit tests failing for irrelevant reason (see #40448).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.75%. Comparing base (69bdf5f) to head (b0c7cbd).
⚠️ Report is 43 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #40457      +/-   ##
============================================
- Coverage     59.04%   58.75%   -0.29%     
+ Complexity    15624    13920    -1704     
============================================
  Files          2797     2584     -213     
  Lines        280750   271511    -9239     
  Branches      12488    11243    -1245     
============================================
- Hits         165764   159531    -6233     
+ Misses       108540   105979    -2561     
+ Partials       6446     6001     -445     

Flag	Coverage Δ
java	65.27% <ø> (-0.17%)	⬇️

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