[observability] add coredns dashboard

Author: sagor999

operations/observability/mixins/workspace/dashboards.libsonnet

@@ -16,5 +16,6 @@
     'gitpod-component-ws-manager.json': (import 'dashboards/components/ws-manager.json'),
     'gitpod-component-ws-proxy.json': (import 'dashboards/components/ws-proxy.json'),
     'gitpod-workspace-success-criteria.json': (import 'dashboards/success-criteria.json'),
+    'gitpod-workspace-coredns.json': (import 'dashboards/coredns.json'),
   },
 }