add loki to grafana

manifests/metrics/grafana/loki-datasource.yaml

@@ -0,0 +1,17 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: loki-grafana-ds
+  namespace: metrics
+  labels:
+    grafana_datasource: "1"
+data:
+  datasource.yaml: |
+    apiVersion: 1
+    datasources:
+      - access: proxy
+        isDefault: false
+        name: Loki
+        type: loki
+        uid: Loki
+        url: http://loki.metrics.svc.cluster.local:3100