ability to override virtual service services

By default these virtual services go to the same place, btu we can override them in the umbrella now:

$ helm template --debug . --generate-name 
...
# Source: istio/templates/kiali-vs.yaml
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: kiali
  namespace: default
spec:
  hosts:
  - "kiali.bigbang.dev"
  gateways:
  - main.default.svc.cluster.local
  http:
  - route:
    - destination:
        port:
          number: 20001
        host: kiali.{{ .Release.Namespace}}.svc.cluster.local

or

$ helm template --debug . --generate-name  --set ingress.kiali.service=haproxy --set ingress.kiali.namespace=haproxy
...
# Source: istio/templates/kiali-vs.yaml
apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: kiali
  namespace: default
spec:
  hosts:
  - "kiali.bigbang.dev"
  gateways:
  - main.default.svc.cluster.local
  http:
  - route:
    - destination:
        port:
          number: 20001
        host: haproxy.haproxy.svc.cluster.local