feat: Add Feature Service Create/delete REST apis and UI

[ntkathole]

What this PR does / why we need it:

This PR adds REST create/delete for feature services and a matching Feast UI create flow. Incomplete projections (view name only, or optional feature subset) are resolved in core via FeatureService.prepare_for_apply() using the same constructor + infer_features path as FeatureStore.apply, so REST/gRPC stay thin and GET returns fully populated featureColumns.

Also, added delete functionality on entity, data sources and feature view.

Screen.Recording.2026-07-18.at.12.07.07.PM.mov

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 76.41509% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.73%. Comparing base (e0a8573) to head (bc8ef89).

Files with missing lines	Patch %	Lines
sdk/python/feast/feature_service.py	70.31%	14 Missing and 5 partials ⚠️
...python/feast/api/registry/rest/feature_services.py	89.74%	2 Missing and 2 partials ⚠️
sdk/python/feast/infra/registry/snowflake.py	0.00%	1 Missing ⚠️
sdk/python/feast/infra/registry/sql.py	0.00%	1 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6612      +/-   ##
==========================================
+ Coverage   45.64%   45.73%   +0.09%     
==========================================
  Files         412      412              
  Lines       48761    48855      +94     
  Branches     6913     6931      +18     
==========================================
+ Hits        22257    22344      +87     
+ Misses      24957    24956       -1     
- Partials     1547     1555       +8     

Flag	Coverage Δ
go-feature-server	30.58% <ø> (ø)
python-unit	47.01% <76.41%> (+0.09%)	⬆️

Files with missing lines	Coverage Δ
sdk/python/feast/infra/registry/registry.py	58.38% <100.00%> (+0.79%)	⬆️
sdk/python/feast/infra/registry/snowflake.py	39.49% <0.00%> (-0.08%)	⬇️
sdk/python/feast/infra/registry/sql.py	57.87% <0.00%> (-0.09%)	⬇️
...python/feast/api/registry/rest/feature_services.py	82.71% <89.74%> (+9.63%)	⬆️
sdk/python/feast/feature_service.py	81.01% <70.31%> (-7.53%)	⬇️

... and 2 files with indirect coverage changes

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