chore: Basic e2e test for go grpc server

[pyalex]

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

What this PR does / why we need it:

Very basic test (but better than nothing) that starts go feature server (GRPC) in a separate thread (since it's blocking) and checks (via grpc client) that it responses on GetOnlineFeatures requests.

Which issue(s) this PR fixes:

Fixes #

[codecov-commenter]

Codecov Report

Merging #2628 (2f1923a) into master (2b2a76b) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2628      +/-   ##
==========================================
+ Coverage   81.39%   81.45%   +0.06%     
==========================================
  Files         161      162       +1     
  Lines       13314    13380      +66     
==========================================
+ Hits        10837    10899      +62     
- Misses       2477     2481       +4     

Flag	Coverage Δ
integrationtests	71.98% <100.00%> (-0.20%)	⬇️
unittests	59.51% <48.48%> (-0.31%)	⬇️

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

Impacted Files	Coverage Δ
...ython/feast/embedded_go/online_features_service.py	96.11% <100.00%> (+1.06%)	⬆️
...on/tests/integration/e2e/test_go_feature_server.py	100.00% <100.00%> (ø)
sdk/python/tests/utils/online_read_write_test.py	93.54% <0.00%> (-6.46%)	⬇️
.../integration/online_store/test_online_retrieval.py	96.84% <0.00%> (-3.16%)	⬇️

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[pyalex]

Improved GIL handling, so that all go calls would release GIL

[felixwang9817]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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