direct: Implement NetworkSecurityBackendAuthenticationConfig controller

[ada-coder-bot]

This PR implements the direct controller, E2E fixtures, and fuzzer for the NetworkSecurityBackendAuthenticationConfig resource.

Summary of Changes:

• Direct Controller: Added the adapter reconciliation logic (Find, Create, Update, Delete, Export) under pkg/controller/direct/networksecurity/.
• Fuzzer: Implemented and registered a KRM fuzzer under pkg/controller/direct/networksecurity/ to test and validate Spec & Status roundtripping.
• Mock Service Extension: Implemented the mock GCP endpoints for BackendAuthenticationConfig inside mockgcp/mocknetworksecurity/.
• Testing & Scaffolding: Added -minimal and -maximal E2E fixtures and recorded golden HTTP and Kubernetes object status outputs.
• Harness Whitelisting: Added the resource kind to the mock GCP whitelisting logic in config/tests/samples/create/harness.go.

This PR was generated by the overseer,overseer,greenfield,step/controller agent (powered by the gemini-3.5-flash model).

Fixes #11894

[argus-watcher-bot]

🤖 AI Factory started investigating CI check failures for this pull request.

[ada-coder-bot]

Investigating validate-generated-files failure

Run: 30078072196
Name: validate-generated-files
Cause: Code Error
Details: The validation check detected that pkg/controller/resourceconfig/static_config.go was out-of-date because NetworkSecurityBackendAuthenticationConfig was not sorted in correct alphabetical order (it should come after NetworkSecurityAuthzPolicy alphabetically).
Action Taken: Ran python3 dev/tasks/generate_static_config.py to regenerate the static config with correct alphabetical ordering.

Investigating unit-tests failure

Run: 30078072196
Name: unit-tests
Cause: Test Failure
Details: The API check test TestCRDFieldPresenceInTestsForAlpha failed because the recently introduced -maximal and -minimal tests for NetworkSecurityBackendAuthenticationConfig provide coverage for .spec.description, .spec.labels, .spec.location, .spec.projectRef, and .spec.wellKnownRoots fields, meaning they are no longer missing and their corresponding entries in the exceptions list tests/apichecks/testdata/exceptions/alpha-missingfields.txt had become out-of-date.
Action Taken: Regenerated the alpha exceptions list with WRITE_GOLDEN_OUTPUT=1 go test ./tests/apichecks/... -run TestCRDFieldPresenceInTestsForAlpha to match the newly added test coverage.

Investigating presubmit-gatekeeper failure

Run: 30078072196
Name: presubmit-gatekeeper
Cause: Infrastructure
Details: This gating check failed downstream of the failures in validate-generated-files and unit-tests.
Action Taken: None (it will pass automatically when the other checks are resolved).

All fixes have been committed and force-pushed to the remote branch to trigger a clean run of the CI pipeline.

(This report was generated by overseer)

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🤖 AI Factory started resolving merge conflicts / rebasing this pull request in a sandbox.

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🤖 AI Factory started resolving merge conflicts / rebasing this pull request in a sandbox.

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🤖 AI Factory started resolving merge conflicts / rebasing this pull request in a sandbox.

[argus-watcher-bot]

🤖 AI Factory started resolving merge conflicts / rebasing this pull request in a sandbox.

[google-oss-prow]

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