feat: add pod annotations for prometheus scrape

Author: jnywong

helm/jupyterhub-cost-monitoring/values.yaml

@@ -45,6 +45,9 @@ serviceAccount:
 service:
   type: ClusterIP
   port: 80
+  annotations:
+    prometheus.io/scrape: "true"
+    prometheus.io/port: "80"
 
 # Ingress resource
 # -----------------------------------------------------------------------------