Implement `spec.uid` for `GrafanaDashboard`

[Baarsgaard]

Followed the same pattern as #1686 for the CustomUID. As discussed in the weekly sync, spec.uid or metadata.uid will always overwrite dashboardModel.uid.

Thanks to the existing Status.UID update detection, existing dashboards are automatically migrated to using metadata.uid by the operator.

Local procedure for testing

Chainsaw tests

make e2e-local-gh-actions TESTS=immutable_uids

Manual

make start-kind
make deploy
kind export kubeconfig --name kind-grafana

# Test resources
kubectl apply -f https://raw.githubusercontent.com/grafana-operator/grafana-operator/master/examples/basic/resources.yaml
kubectl apply -f ../test-dashboard.yaml

# Check status:
# dashboards
#   - default/dashboard-uid/dashUID
kubectl get grafanas -A -o yaml

# Build and apply image to cluster
make ko-build-kind
IMG=ko.local/grafana/grafana-operator make deploy
kubectl patch deploy -n grafana-operator-system grafana-operator-controller-manager-v5  --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/imagePullPolicy", "value":"IfNotPresent"}]'

# Check status:
# dashboards
#   - default/dashboard-uid/dashUID -> specUID
kubectl get grafanas -A -o yaml

../test-dashboard.yaml

apiVersion: grafana.integreatly.org/v1beta1
kind: GrafanaDashboard
metadata:
  name: dashboard-uid
spec:
  instanceSelector:
    matchLabels:
      dashboards: "grafana"
  uid: specUID
  resyncPeriod: 10s
  json: >
    {
      "id": null,
      "uid": "dashUID",
      "title": "Simple Dashboard",
      "tags": [],
      "style": "dark",
      "timezone": "browser",
      "editable": true,
      "hideControls": false,
      "graphTooltip": 1,
      "panels": [],
      "time": {
        "from": "now-6h",
        "to": "now"
      },
      "timepicker": {
        "time_options": [],
        "refresh_intervals": []
      },
      "templating": {
        "list": []
      },
      "annotations": {
        "list": []
      },
      "refresh": "5s",
      "schemaVersion": 17,
      "version": 0,
      "links": []
    }

• [x] Chainsaw tests for immutability of spec.uid
• [x] Chainsaw tests for expected status on Grafana instance
• [ ] Update dashboard UID documentation