Enable Apache Iceberg REST Metrics Reporting for Lakehouse

[feefs]

According to https://docs.cloud.google.com/lakehouse/docs/release-notes#May_07_2026, we no longer need to override rest-metrics-reporting-enabled to false.

[github-actions]

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[github-actions]

Assigning reviewers:

R: @jrmccluskey for label python.
R: @kennknowles for label java.

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[derrickaw]

Those last two checks are currently red on master, so have to wait until green:
https://github.com/apache/beam/actions/workflows/beam_PreCommit_Portable_Python.yml
https://github.com/apache/beam/actions/workflows/beam_PreCommit_PythonDocker.yml

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 55.94%. Comparing base (eea1e03) to head (b13ab67).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #39650      +/-   ##
============================================
- Coverage     55.95%   55.94%   -0.01%     
  Complexity     2272     2272              
============================================
  Files          1112     1113       +1     
  Lines        175063   175064       +1     
  Branches       1458     1458              
============================================
- Hits          97959    97947      -12     
- Misses        74645    74658      +13     
  Partials       2459     2459              

Flag	Coverage Δ
python	79.85% <ø> (-0.02%)	⬇️

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