Update Grafana dashboard to the latest (radius-project#5518)

# Description

Update Grafana dashboard to the latest

## Issue reference

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Fixes: radius-project#5517

## Checklist

Please make sure you've completed the relevant tasks for this PR, out of
the following list:

* [ ] Code compiles correctly
* [ ] Adds necessary unit tests for change
* [ ] Adds necessary E2E tests for change
* [ ] Unit tests passing
* [ ] Extended the documentation / Created issue for it

grafana/README.md

@@ -1,3 +1,6 @@
-Monitoring Dashboard
+# Grafana dashboard
 
-This includes dashboard templates to monitor radius system. 
+This includes the following dashboard templates to monitor Radius services:
+
+* [Radius overview dashboard](./radius-overview-dashboard.json) : This dashboard template overviews each Radius service.
+* [Radius resource provider dashboard](./radius-resource-provider-dashboard.json) : This dashboard template shows the detail status of each Radius service.