Add InfraDiff class for feast plan

[felixwang9817]

What this PR does / why we need it: This PR adds the InfraDiff class and adds support for Infra objects to the Registry.

Which issue(s) this PR fixes:

Fixes #

Does this PR introduce a user-facing change?:

NONE

[codecov-commenter]

Codecov Report

Merging #2190 (5a2905a) into master (d447db2) will decrease coverage by 0.07%.
The diff coverage is 77.27%.

@@            Coverage Diff             @@
##           master    #2190      +/-   ##
==========================================
- Coverage   84.61%   84.53%   -0.08%     
==========================================
  Files         102      104       +2     
  Lines        8207     8239      +32     
==========================================
+ Hits         6944     6965      +21     
- Misses       1263     1274      +11     

Flag	Coverage Δ
integrationtests	74.24% <69.56%> (-0.35%)	⬇️
unittests	59.02% <77.27%> (+0.03%)	⬆️

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

Impacted Files	Coverage Δ
sdk/python/feast/registry.py	85.18% <30.00%> (-1.93%)	⬇️
sdk/python/feast/diff/infra_diff.py	85.00% <85.00%> (ø)
sdk/python/feast/diff/FcoDiff.py	88.46% <100.00%> (-2.02%)	⬇️
sdk/python/feast/diff/utils.py	100.00% <100.00%> (ø)
sdk/python/feast/infra/utils/aws_utils.py	85.50% <0.00%> (-0.73%)	⬇️

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[achals]

Can you update the commit message/PR title should be more descriptive

[achals]

Can you also print out what feast plan produces when infra is changed in the PR description?

[feast-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[felixwang9817]

Can you also print out what feast plan produces when infra is changed in the PR description?

this PR doesn't actually change the output of feast plan

[adchia]

/lgtm