docs: Add end-to-end registry deletion lifecycle example and unit test (#5360) by obielin · Pull Request #6504 · feast-dev/feast

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The existing registry deletion docs cover the CLI and individual Python
SDK delete methods, but lack a single copy-pasteable example showing the
full create -> verify -> delete -> confirm flow.

- Add an 'End-to-end example' snippet to registry.md that lists a feature
  view, deletes it with delete_feature_view(), and lists again to confirm.
- Add a unit test for FeatureView deletion via apply(objects_to_delete=...,
  partial=False) to guard the programmatic deletion path.

Signed-off-by: Linda Oraegbunam <obielinda@gmail.com>