Change internal references from input to batch_source

[felixwang9817]

Signed-off-by: Felix Wang wangfelix98@gmail.com

What this PR does / why we need it: FeatureViews have always required a batch data source as input; this argument is currently named input. We recently introduced stream sources here, so now we have three arguments: a required input, an optional batch_source, and an optional stream_source. We should remove input as an argument, make batch_source required, and leave stream_source optional; this is a breaking change, so we prepare for it by adding a deprecation warning. We also change internal references and docs to use batch_source instead of input, to point people in the right direction.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

There is now a deprecation warning in FeatureView.

[codecov-commenter]

Codecov Report

Merging #1729 (cd0c62d) into master (bf557bc) will decrease coverage by 17.29%.
The diff coverage is 89.28%.

@@             Coverage Diff             @@
##           master    #1729       +/-   ##
===========================================
- Coverage   79.06%   61.77%   -17.30%     
===========================================
  Files          80       78        -2     
  Lines        6849     6762       -87     
===========================================
- Hits         5415     4177     -1238     
- Misses       1434     2585     +1151     

Flag	Coverage Δ
integrationtests	?
unittests	61.77% <89.28%> (+0.01%)	⬆️

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

Impacted Files	Coverage Δ
sdk/python/feast/repo_operations.py	31.33% <0.00%> (ø)
...alization/test_offline_online_store_consistency.py	58.24% <ø> (-41.76%)	⬇️
...gration/offline_store/test_historical_retrieval.py	50.17% <ø> (-48.78%)	⬇️
...sts/integration/registration/test_feature_store.py	68.38% <ø> (-31.62%)	⬇️
...on/tests/integration/registration/test_registry.py	69.56% <ø> (-30.44%)	⬇️
...ests/integration/scaffolding/test_partial_apply.py	50.00% <ø> (-50.00%)	⬇️
sdk/python/feast/feature_view.py	84.61% <90.00%> (-4.37%)	⬇️
sdk/python/feast/feature_store.py	91.33% <100.00%> (-2.17%)	⬇️
sdk/python/feast/inference.py	58.33% <100.00%> (-31.26%)	⬇️
sdk/python/feast/infra/local.py	92.15% <100.00%> (ø)
... and 41 more

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[achals]

/lgtm

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[APPROVALNOTIFIER] This PR is APPROVED

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

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[felixwang9817]

/retest

[tedhtchang]

@felixwang9817 Should we warn users only when the input is assigned ?

[felixwang9817]

@tedhtchang That's a good point, I think ideally we would have done that. However, given that (a) input was a required parameter before this change, so almost all users will continue to use input, and (b) releases are fairly frequent so this deprecation warning will soon become outdated, I think we can leave this change as is.

[felixwang9817]

@tedhtchang btw, I managed to insert this change into a separate PR (#1746). Thanks for pointing this one out!

[tedhtchang]

@felixwang9817 Thanks. Looks good.