feat: Offline write batch support for IcebergSource

[ntkathole]

What this PR does / why we need it:

When a FeatureView's batch_source is an IcebergSource, calling fs.write_to_offline_store() or fs.push(to=PushMode.ONLINE_AND_OFFLINE) was not supported.

Added Offline write batch support for IcebergSource.

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 9.09091% with 30 lines in your changes missing coverage. Please review.
✅ Project coverage is 47.60%. Comparing base (5ee7ee3) to head (71a94d6).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
sdk/python/feast/infra/offline_stores/duckdb.py	8.69%	21 Missing ⚠️
...ffline_stores/contrib/spark_offline_store/spark.py	10.00%	9 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6829      +/-   ##
==========================================
- Coverage   47.61%   47.60%   -0.02%     
==========================================
  Files         422      422              
  Lines       52346    52391      +45     
  Branches     7596     7605       +9     
==========================================
+ Hits        24925    24939      +14     
- Misses      25646    25676      +30     
- Partials     1775     1776       +1     

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	48.93% <9.09%> (-0.02%)	⬇️

Files with missing lines	Coverage Δ
...ffline_stores/contrib/spark_offline_store/spark.py	35.63% <10.00%> (-0.37%)	⬇️
sdk/python/feast/infra/offline_stores/duckdb.py	35.27% <8.69%> (-1.92%)	⬇️

... and 3 files with indirect coverage changes

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[jyejare]

LGTM, nitpck comment.