avoid using transactions on OSS Redis

[DvirDukhan]

Signed-off-by: DvirDukhan dvir@redis.com

What this PR does / why we need it:
This PR avoids using Transactions in redis-py pipelines when on a single instance mode.
redis-py pipelines are created by default as transactions https://github.com/redis/redis-py/blob/24cdd70761c7c275d5010f628f83d919bf35fc90/redis/client.py#L1020
However, on cluster mode, redis-py pipeline is built with transaction=None https://github.com/redis/redis-py/blob/045d5ed15305ccc44a0330e6f65f669998815598/redis/cluster.py#L698
from https://redis.io/topics/transactions :

All the commands in a transaction are serialized and executed sequentially.
It can never happen that a request issued by another client is served in the middle of the execution of a Redis transaction.
This guarantees that the commands are executed as a single isolated operation.

This could change can help increasing throughput when accessing a single Redis instance with multiple Feast clients.

Does this PR introduce a user-facing change?:

NONE

CC @chayim

[codecov-commenter]

Codecov Report

Merging #2296 (3720d6e) into master (b86a99b) will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2296      +/-   ##
==========================================
+ Coverage   86.01%   86.06%   +0.05%     
==========================================
  Files         116      116              
  Lines        9820     9820              
==========================================
+ Hits         8447     8452       +5     
+ Misses       1373     1368       -5     

Flag	Coverage Δ
integrationtests	74.78% <100.00%> (-0.26%)	⬇️
unittests	58.55% <0.00%> (ø)

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/redis.py	94.83% <100.00%> (ø)
.../integration/online_store/test_universal_online.py	97.17% <0.00%> (+0.40%)	⬆️
sdk/python/feast/infra/online_stores/datastore.py	90.56% <0.00%> (+1.88%)	⬆️

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[adchia]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: adchia, DvirDukhan

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