Implement direct Helm-based istiod installation in cluster-ingress-operator to remove dependency on OLM and the sail-operator.

Acceptance Criteria

• istiod installs via Helm without OLM when GatewayClass is created
• Seamless upgrade/downgrade between OLM-based and Helm-based installations
• All existing E2E tests pass with no regressions

References

• Enhancement: `enhancements/ingress/gateway-api-without-olm.md
• Parent epic: NE-2286
• User story: NE-2470
• Spike: NE-2437
• POC PR: https://github.com/openshift/cluster-ingress-operator/pull/1347
• OSSM POC: https://github.com/openshift/cluster-ingress-operator/pull/1351