fix: Fix incorrect on demand feature view diffing and improve Java tests

[adchia]

What this PR does / why we need it:
There was an issue with diffing on demand feature views casting the wrong proto to OnDemandFeatureViewSpec. This was not caught for two reasons:

• There is no Python unit test testing that diff logic (or an integration test testing changing an existing odfv)
• The Java tests also started breaking, but in a silent way. This was caused by the tests relying on a checked in registry, which does not change between PRs. This PR now sets it up so that that registry is dynamically generated by Maven during tests.

I haven't fully tested that the GitHub actions workflows work yet (because it requires we now also install Python on the workflows and the GitHub workflows aren't easy to test).

Which issue(s) this PR fixes:

Fixes #

[felixwang9817]

/lgtm

[codecov-commenter]

Codecov Report

Merging #3074 (73394ed) into master (36747aa) will decrease coverage by 9.21%.
The diff coverage is 77.77%.

@@            Coverage Diff             @@
##           master    #3074      +/-   ##
==========================================
- Coverage   67.35%   58.13%   -9.22%     
==========================================
  Files         169      203      +34     
  Lines       14834    16839    +2005     
==========================================
- Hits         9992     9790     -202     
- Misses       4842     7049    +2207     

Flag	Coverage Δ
integrationtests	?
unittests	58.13% <77.77%> (?)

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

Impacted Files	Coverage Δ
sdk/python/tests/unit/diff/test_registry_diff.py	90.32% <76.00%> (+74.10%)	⬆️
sdk/python/feast/diff/registry_diff.py	71.71% <100.00%> (+44.73%)	⬆️
...sts/integration/registration/test_universal_cli.py	20.20% <0.00%> (-79.80%)	⬇️
...ts/integration/offline_store/test_offline_write.py	26.08% <0.00%> (-73.92%)	⬇️
...fline_store/test_universal_historical_retrieval.py	28.75% <0.00%> (-71.25%)	⬇️
...ests/integration/e2e/test_python_feature_server.py	29.50% <0.00%> (-70.50%)	⬇️
...dk/python/tests/integration/e2e/test_validation.py	27.55% <0.00%> (-69.30%)	⬇️
...s/integration/registration/test_universal_types.py	32.25% <0.00%> (-67.75%)	⬇️
sdk/python/feast/infra/online_stores/redis.py	28.39% <0.00%> (-66.58%)	⬇️
sdk/python/tests/integration/e2e/test_usage_e2e.py	33.87% <0.00%> (-66.13%)	⬇️
... and 158 more

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[felixwang9817]

/lgtm

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[feast-ci-bot]

New changes are detected. LGTM label has been removed.