Change RedisBackedJobService to use a connection pool

[zhilingc]

What this PR does / why we need it:
Current implementation of connection to jobs redis is using a client that upon failure does not refresh its connection to the db - so if anything goes awry batch retrieval is unusable until the instance is restarted to manually establish a new connection with redis.

This PR changes RedisBackedJobService to use a connection pool instead.

Which issue(s) this PR fixes:

N/A

Does this PR introduce a user-facing change?:

NONE

[khorshuheng]

/lgtm

[khorshuheng]

/approve

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: khorshuheng, zhilingc

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[brandon733]

not sure if this is bc of this change, but to get minikube working w basic.ipynb, I had to do:

diff --git a/infra/charts/feast/values-demo.yaml b/infra/charts/feast/values-demo.yaml
index fad4bc0..eee063d 100644
--- a/infra/charts/feast/values-demo.yaml
+++ b/infra/charts/feast/values-demo.yaml
@@ -62,6 +62,9 @@ feast-serving-online:
   store.yaml:
     name: redis
     type: REDIS
+    redis_config:
+      host: feast.example.com
+      port: 32101
     subscriptions:
       - name: "*"
         project: "*"

o/w ingest() would fail w/ cannot conn to redis

[khorshuheng]

@b133t Which image version are you using?

[brandon733]

0.4.3
minikube setup as detailed in https://docs.feast.dev/getting-started/installing-feast#minikube
then running basic.ipynb in source repo w/ jupyter (without batch)
fails on "7. Ingest data into Feast for a feature set", unless make change above (and s/feast.example.com/$(minikube ip)/ + rerun helm)