Use Online Boutique's Istio Kustomize Component

[NimJay]

• Online Boutique is introducing a new Kustomize Component for its Istio (and Anthos Service Mesh [ASM]) resources.
• See https://github.com/GoogleCloudPlatform/microservices-demo/pull/1601.
• The /istio-manifests folder (in Online Boutique) will eventually be deleted.
• We should make sure Cloud Ops Sandbox isn't using the /istio-manifests folder.
• Instead, Cloud Ops Sandbox should use the new Kustomize Component for Istio and Anthos Service Mesh.
• We can make this change once https://github.com/GoogleCloudPlatform/microservices-demo/pull/1601 is merged.