charts,salt: Set UID for grafana datasources

Since in newer grafana version we need to use the datasource UID to
reference it, we explicitly set the datasource UID from ConfigMap so
that it's easier to reference them.

Re-render prometheus-operator salt state using:
```
./charts/render.py prometheus-operator \
  charts/kube-prometheus-stack.yaml \
  charts/kube-prometheus-stack/ \
  --namespace metalk8s-monitoring \
  --service-config grafana \
  metalk8s-grafana-config \
  metalk8s/addons/prometheus-operator/config/grafana.yaml \
  metalk8s-monitoring \
  --service-config prometheus \
  metalk8s-prometheus-config \
  metalk8s/addons/prometheus-operator/config/prometheus.yaml \
  metalk8s-monitoring \
  --service-config alertmanager \
  metalk8s-alertmanager-config \
  metalk8s/addons/prometheus-operator/config/alertmanager.yaml \
  metalk8s-monitoring \
  --service-config dex \
  metalk8s-dex-config \
  metalk8s/addons/dex/config/dex.yaml.j2 metalk8s-auth \
  --drop-prometheus-rules charts/drop-prometheus-rules.yaml \
  --patch 'PrometheusRule,metalk8s-monitoring,prometheus-operator-kubernetes-system-kubelet,spec:groups:0:rules:1:for,"5m"' \
  > salt/metalk8s/addons/prometheus-operator/deployed/chart.sls
```

CHANGELOG.md

@@ -97,6 +97,9 @@
   metalk8s-sosreport package compatible with sos version 4.0+
   (PR[#3664](https://github.com/scality/metalk8s/pull/3664))
 
+- Explicitly set the Grafana datasource UID to `metalk8s-<datasource_name>`
+  (PR[#3668](https://github.com/scality/metalk8s/pull/3668))
+
 ## Bug fixes
 
 - [#3601](https://github.com/scality/metalk8s/issues/3601) - Marks

charts/kube-prometheus-stack.yaml

@@ -165,8 +165,20 @@ grafana:
         foldersFromFilesStructure: true
 
     datasources:
+      # NOTE: We do not deploy default datasource as we want to set UID
+      # and it's not possible using this template
+      defaultDatasourceEnabled: false
+
+  additionalDataSources:
+    - name: Prometheus
+      uid: metalk8s-prometheus
+      type: prometheus
+      access: proxy
+      isDefault: true
       # Service deployed by Thanos
       url: http://thanos-query-http:10902/
+      jsonData:
+        timeInterval: 30s
 
   nodeSelector:
     node-role.kubernetes.io/infra: ''

salt/metalk8s/addons/logging/loki/deployed/datasource.sls

@@ -19,6 +19,7 @@ Deploy ConfigMap for Loki datasource:
             apiVersion: 1
             datasources:
             - name: Loki
+              uid: metalk8s-loki
               type: loki
               access: proxy
               url: http://loki.metalk8s-logging.svc.cluster.local:3100/

salt/metalk8s/addons/prometheus-operator/deployed/chart.sls

@@ -25089,13 +25089,14 @@ data:
   datasource.yaml: |-
     apiVersion: 1
     datasources:
-    - name: Prometheus
-      type: prometheus
-      url: http://thanos-query-http:10902/
-      access: proxy
+    - access: proxy
       isDefault: true
       jsonData:
         timeInterval: 30s
+      name: Prometheus
+      type: prometheus
+      uid: metalk8s-prometheus
+      url: http://thanos-query-http:10902/
 kind: ConfigMap
 metadata:
   labels: