Add consistent hash policy support to TrafficPolicy

Normalized profile

What this task asks for

Add spec.consistentHash to TrafficPolicy and merge it into route hash_policy generation. `disable` - bool that suppresses consistent hashing on a route; when true, no other fields may be set. `headers` - array of objects, each with `headerName`, optional `regexRewrite` (with `pattern` and `substitution`), and `terminal`. When `consistentHash` is set (even as empty `{}`), the `RouteAction` must include `hash_policy` entries. If no sub-fields are specified, default to a single sourceIp hash policy with terminal=false. When `disable` is true, no hash policies are produced and any inherited from broader-scoped policies are suppressed. When a header has `regexRewrite` set, the header value is rewritten using the regex before hashing. Merge metadata must record this field as `consistentHash` under the existing TrafficPolicy merge metadata key.