Refactor the datastore online_read method to be slightly more efficient

[achals]

Signed-off-by: Achal Shah achals@gmail.com

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

none

[codecov-commenter]

Codecov Report

Merging #1819 (a960eee) into master (e895bc4) will decrease coverage by 20.93%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           master    #1819       +/-   ##
===========================================
- Coverage   84.84%   63.91%   -20.94%     
===========================================
  Files          92       89        -3     
  Lines        6844     6718      -126     
===========================================
- Hits         5807     4294     -1513     
- Misses       1037     2424     +1387     

Flag	Coverage Δ
integrationtests	?
unittests	63.91% <0.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
sdk/python/feast/infra/online_stores/datastore.py	30.32% <0.00%> (-63.17%)	⬇️
.../integration/online_store/test_universal_online.py	16.32% <0.00%> (-83.68%)	⬇️
.../integration/online_store/test_online_retrieval.py	17.39% <0.00%> (-82.61%)	⬇️
sdk/python/tests/utils/online_read_write_test.py	18.18% <0.00%> (-81.82%)	⬇️
...fline_store/test_universal_historical_retrieval.py	20.25% <0.00%> (-79.75%)	⬇️
...gration/registration/test_feature_service_apply.py	31.25% <0.00%> (-68.75%)	⬇️
...hon/tests/integration/registration/test_cli_gcp.py	31.70% <0.00%> (-68.30%)	⬇️
...n/tests/integration/registration/test_cli_redis.py	32.55% <0.00%> (-67.45%)	⬇️
sdk/python/feast/infra/online_stores/redis.py	30.35% <0.00%> (-64.29%)	⬇️
sdk/python/feast/infra/online_stores/dynamodb.py	30.37% <0.00%> (-60.76%)	⬇️
... and 38 more

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[felixwang9817]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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