support multiple regions when using PreferLocal/WeightedZones

Description: Enable locality_weighted_lb_config for ConsistentHash load balancer type (Maglev/RingHash) in Envoy Gateway, which is already supported by upstream Envoy but not exposed in Envoy Gateway's API.

Use Case: Session affinity with locality preference

Locality-weighted consistent hashing where:

• ✅ Hash(Session-ID) → picks specific endpoint
• ✅ Endpoint is in a specific zone → always same zone
• ✅ Locality weights control the distribution (e.g., 70% in Zone A)

Envoy Gateway's code explicitly:

1. Doesn't include LocalityLbConfig when building Maglev clusters (missing in xDS translation)

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