Add assertions for supported sources for known online stores

[achals]

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

What this PR does / why we need it:
Adds some assertions, and fixes some minor bugs with prints and removes a dangling reference to the redis provider.
Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[feast-ci-bot]

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[codecov-commenter]

Codecov Report

Merging #1648 (c78ceda) into master (c63b037) will increase coverage by 0.06%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master    #1648      +/-   ##
==========================================
+ Coverage   83.39%   83.46%   +0.06%     
==========================================
  Files          71       71              
  Lines        6113     6144      +31     
==========================================
+ Hits         5098     5128      +30     
- Misses       1015     1016       +1     

Flag	Coverage Δ
integrationtests	83.39% <66.66%> (+0.07%)	⬆️
unittests	76.56% <66.66%> (+0.11%)	⬆️

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/helpers.py	79.41% <ø> (ø)
sdk/python/feast/repo_operations.py	32.35% <50.00%> (+0.17%)	⬆️
sdk/python/feast/repo_config.py	95.90% <100.00%> (ø)
sdk/python/feast/infra/online_stores/datastore.py	78.70% <0.00%> (-0.39%)	⬇️
sdk/python/tests/test_online_retrieval.py	100.00% <0.00%> (ø)
sdk/python/feast/online_response.py	97.43% <0.00%> (+0.21%)	⬆️

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[feast-ci-bot]

@achals: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
test-telemetry	c78ceda	link	/test test-telemetry

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[achals]

Closing this in favor of #1649