fix: preserve localityLbSetting.enabled=false in Istio destination rules

[kei-gnu]

Related #1719

Summary

LocalityLbSetting.Enabled is a plain bool with omitempty, so an explicit enabled: false in trafficPolicy.loadBalancer.localityLbSetting is dropped from the generated DestinationRules (localityLbSetting: {}).

Istio treats an unset enabled as the mesh-wide default (enabled), and locality failover is activated whenever outlierDetection is set. Users who set enabled: false to keep traffic evenly distributed across zones silently end up with zone-prioritized routing.

Changes

• Changed LocalityLbSetting.Enabled from bool to *bool so that false round-trips into the DestinationRule (regenerated deepcopy)
• Added a regression test (TestIstioRouter_LocalityLbSettingEnabledFalse)
• No CRD change: enabled is already declared as boolean

Testing

Verified locally against kind (Kubernetes 1.35.1) with Istio 1.29.2, using a Flagger image built from this branch.
A Canary with:

trafficPolicy:
  loadBalancer:
    simple: RANDOM
    localityLbSetting:
      enabled: false
  outlierDetection:
    consecutive5xxErrors: 5
    interval: 10s
    baseEjectionTime: 10s

With v1.44.0 the generated podinfo-primary / podinfo-canary DestinationRules lose the flag:

  trafficPolicy:
    loadBalancer:
      localityLbSetting: {}
      simple: RANDOM

With this branch both DestinationRules keep it:

  trafficPolicy:
    loadBalancer:
      localityLbSetting:
        enabled: false
      simple: RANDOM
    outlierDetection:
      baseEjectionTime: 10s
      consecutive5xxErrors: 5
      interval: 10s

Also confirmed on the client sidecar (pilot-agent request GET clusters, two zone-labelled nodes) that the endpoints are no longer split into priority: 0/1 by zone once the flag reaches Istio.