Using meta labels in VMServiceScrape's label selector

[kyu-clover]

It would be nice for VMServiceScrape's selector, if it can use meta labels defined in kubernetes_sd_configs, i.e. __meta_kubernetes_service_annotation_<annotationname>. So we can have something like

apiVersion: operator.victoriametrics.com/v1beta1
kind: VMServiceScrape
metadata:
  name: stackdriver-scrape
spec:
  selector:
    matchLabels:
      __meta_kubernetes_service_annotation_prometheus_io_scrape: stackdriver-exporter
  discoveryRole: service
  namespaceSelector:
    matchNames:
      - monitoring
  endpoints:
    - port: http