istio: Add customized metric don't work!

Bug description

• I follow this instruction ‘Customizing Istio Metrics’ to add a new metric ‘request_id’.
• use command kubectl edit envoyfilter -n istio-system stats-filter-1.7 modify value of ‘spec.configPatches[match.context: GATEWAY][patch.value.typed_config.value.config.configuration]’ to {“debug”:true,“metrics”:[{“dimensions”:{"request_id":"request.headers['x-request-id']"},“name”:“requests_total”}],“stat_prefix”:“istio”,“disable_host_header_fallback”: true}
• Use command kubectl apply -f https://raw.githubusercontent.com/istio/istio/release-1.7/samples/addons/prometheus.yaml deploy promethues.
• use command istioctl dashboard prometheus --address=0.0.0.0& to expose service.
• open grafana page
• input metricistio_requests_total
• click Execute Button don’t get any data related to ‘request_id’ tag.

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Expected behavior Get some metric data contains tag request_id. When I try replace tag request_id with default tag,such as request_host,it worked! Sample result as follows. istio_requests_total{app=“istio-ingressgateway”,chart=“gateways”,connection_security_policy=“unknown”,destination_app=“productpage”,destination_canonical_revision=“v1”,destination_canonical_service=“productpage”,destination_principal=“spiffe://cluster.local/ns/book-info/sa/bookinfo-productpage”,destination_service=“productpage.book-info.svc.cluster.local”,destination_service_name=“productpage”,destination_service_namespace=“book-info”,destination_version=“v1”,destination_workload=“productpage-v1”,destination_workload_namespace=“book-info”,heritage=“Tiller”,instance=“10.244.0.91:15090”,istio=“ingressgateway”,job=“kubernetes-pods”,kubernetes_namespace=“istio-system”,kubernetes_pod_name=“istio-ingressgateway-77bcdbf694-9lsg5”,pod_template_hash=“77bcdbf694”,release=“istio”,reporter=“source”,request_host="37a0a958-1d68-4550-8695-67fe5ee888dd",request_protocol=“http”,response_code=“200”,response_flags=“-”,service_istio_io_canonical_name=“istio-ingressgateway”,service_istio_io_canonical_revision=“latest”,source_app=“istio-ingressgateway”,source_canonical_revision=“latest”,source_canonical_service=“istio-ingressgateway”,source_principal=“spiffe://cluster.local/ns/istio-system/sa/istio-ingressgateway-service-account”,source_version=“unknown”,source_workload=“istio-ingressgateway”,source_workload_namespace=“istio-system”}

Version (include the output of istioctl version --remote and kubectl version --short and helm version if you used Helm) 1.7.3 How was Istio installed?

istioctl install  -f - <<EOF
apiVersion: install.istio.io/v1alpha1
kind: IstioOperator
spec:
  meshConfig:
    accessLogFile: /dev/stdout
  values:
    global:
      proxy:
        privileged: true
      tracer:
        zipkin:
          address: zipkin:9411
EOF

Environment where bug was observed (cloud vendor, OS, etc)

[root@k18-2 istio]# uname -r
5.2.4-1.el7.elrepo.x86_64
[root@k18-2 istio]# cat /etc/redhat-release
CentOS Linux release 7.6.1810 (Core)
[root@k18-2 istio]# kubectl version --short
Client Version: v1.18.6
Server Version: v1.18.6
[root@k18-2 istio]# istioctl version
client version: 1.7.3
control plane version: 1.7.3
data plane version: 1.7.3 (13 proxies)