charts,salt: enable Dex metrics

Enable telemetry and re-render dex chart:
```
./charts/render.py dex \
      --namespace metalk8s-auth charts/dex.yaml \
      --service-config dex metalk8s-dex-config \
      metalk8s/addons/dex/config/dex.yaml.j2 metalk8s-auth \
      --remove-manifest Secret dex \
      charts/dex/ > salt/metalk8s/addons/dex/deployed/chart.sls
```

Refs: #3374

charts/dex.yaml

@@ -94,3 +94,6 @@ config:
 
   enablePasswordDB: true
   staticPasswords: []
+
+# Expose metrics for Prometheus
+telemetry: true

salt/metalk8s/addons/dex/deployed/chart.sls

@@ -88,6 +88,9 @@ spec:
   - name: https
     port: 32000
     targetPort: https
+  - name: telemetry
+    port: 37000
+    targetPort: telemetry
   selector:
     app.kubernetes.io/instance: dex
     app.kubernetes.io/name: dex
@@ -147,6 +150,9 @@ spec:
         - containerPort: 5556
           name: https
           protocol: TCP
+        - containerPort: 5558
+          name: telemetry
+          protocol: TCP
         resources: null
         volumeMounts:
         - mountPath: /etc/dex/cfg