chore: Update docstrings for batch materialization engine

[felixwang9817]

Signed-off-by: Felix Wang wangfelix98@gmail.com

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

[achals]

/ok-to-test
/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: achals, felixwang9817

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[codecov-commenter]

Codecov Report

Merging #3091 (7325b24) into master (9f221e6) will increase coverage by 8.77%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3091      +/-   ##
==========================================
+ Coverage   67.12%   75.89%   +8.77%     
==========================================
  Files         173      207      +34     
  Lines       15110    17016    +1906     
==========================================
+ Hits        10142    12914    +2772     
+ Misses       4968     4102     -866     

Flag	Coverage Δ
integrationtests	66.96% <0.00%> (-0.16%)	⬇️
unittests	58.28% <0.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...ra/materialization/batch_materialization_engine.py	86.66% <0.00%> (-2.99%)	⬇️
...s/contrib/trino_offline_store/connectors/upload.py	8.97% <0.00%> (ø)
.../feature_repos/universal/online_store/cassandra.py	42.85% <0.00%> (ø)
...ontrib/postgres_offline_store/tests/data_source.py	51.02% <0.00%> (ø)
...k/python/feast/infra/materialization/lambda/app.py	26.66% <0.00%> (ø)
...line_stores/contrib/postgres_repo_configuration.py	100.00% <0.00%> (ø)
...line_stores/contrib/postgres_repo_configuration.py	100.00% <0.00%> (ø)
...thon/feast/infra/utils/postgres/postgres_config.py	100.00% <0.00%> (ø)
...s/contrib/trino_offline_store/tests/data_source.py	17.64% <0.00%> (ø)
.../online_stores/contrib/hbase_online_store/hbase.py	37.25% <0.00%> (ø)
... and 99 more

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