Istio OL - Configure gateways to use iterable gateway pattern

Motivation

See #2469 (closed) for motivations and an example branch.

Acceptance Criteria

• The public and passthrough gateways must be configured using the iteration pattern
  • The pattern should use a single package
• The existing istio3-public-gateway and istio3-passthrough-gateway packages must be removed
• All values files that are involved in configuring ingress must be updated to use the new gateway