[Java Feature Server] Use hgetall in redis connector when number of retrieved fields is big enough

[pyalex]

Signed-off-by: pyalex moskalenko.alexey@gmail.com

What this PR does / why we need it:

According to my analysis after the number of fields passed to hmget surpasses some value (roughly 50) - hgetall becomes a much more efficient way to retrieve the same data. With 250 fields - hgetall is 5x faster then hmget.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

none

[codecov-commenter]

Codecov Report

Merging #2159 (b3edfcf) into master (a753e73) will decrease coverage by 25.65%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           master    #2159       +/-   ##
===========================================
- Coverage   84.40%   58.75%   -25.66%     
===========================================
  Files         101      101               
  Lines        8098     8107        +9     
===========================================
- Hits         6835     4763     -2072     
- Misses       1263     3344     +2081     

Flag	Coverage Δ
integrationtests	?
unittests	58.75% <ø> (-0.06%)	⬇️

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

Impacted Files	Coverage Δ
.../integration/online_store/test_universal_online.py	15.34% <0.00%> (-82.80%)	⬇️
.../integration/online_store/test_online_retrieval.py	17.39% <0.00%> (-82.61%)	⬇️
...fline_store/test_universal_historical_retrieval.py	19.18% <0.00%> (-80.23%)	⬇️
sdk/python/tests/utils/online_read_write_test.py	20.68% <0.00%> (-79.32%)	⬇️
...gration/registration/test_feature_service_apply.py	31.25% <0.00%> (-68.75%)	⬇️
sdk/python/feast/infra/online_stores/redis.py	26.97% <0.00%> (-67.11%)	⬇️
sdk/python/tests/data/data_creator.py	34.78% <0.00%> (-65.22%)	⬇️
sdk/python/tests/integration/e2e/test_usage_e2e.py	35.00% <0.00%> (-65.00%)	⬇️
...s/integration/registration/test_universal_types.py	36.12% <0.00%> (-62.59%)	⬇️
...istration/test_universal_odfv_feature_inference.py	38.29% <0.00%> (-61.71%)	⬇️
... and 49 more

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[tsotnet]

nit: maybe make this a constant at the beginning of the file so it's better visible?

[pyalex]

Added constant

[tsotnet]

Looks good to me overall

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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