[Draft] feat: add E2E tests for --enable-cross-namespace flag

[sapphirew]

Issue #, if available:

Description of changes:

Regenerate iam-controller using updated code-generator and runtime that introduce the unified --enable-cross-namespace flag with phased rollout.

Generated code changes:

• Renames EnableCrossNamespaceReferences to EnableCrossNamespace
• Updates ValidateCrossNamespaceReference to return (string, bool, error)
• Adds --enable-cross-namespace flag to Helm deployment template
• Adds enableCrossNamespace: true to Helm values (Phase 1 default)

E2E tests cover three scenarios:

• flag=true (Phase 1 default): cross-namespace ref succeeds with ACK.CrossNamespaceDeprecation condition as deprecation warning
• flag=false: cross-namespace ref rejected with ACK.Terminal condition containing the --enable-cross-namespace flag name
• same-namespace: ref always succeeds regardless of flag value with no deprecation condition present

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[ack-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: sapphirew
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[ack-prow]

@sapphirew: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
iam-verify-code-gen	475c24e	link	true	/test iam-verify-code-gen
iam-kind-e2e	475c24e	link	true	/test iam-kind-e2e

Full PR test history. Your PR dashboard.

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[kprahulraj]

Doc changes is added - aws-controllers-k8s/docs#37