fix(argocd): multisource patch doc, Ingress grafana-onelab

- Root cause: live Application kept spec.source; Argo ignored observability chart
- Add jsonpatch-multisource.json + argocd/README.md migration steps
- Grafana: disable subchart ingress; add templates/ingress-grafana-onelab.yaml

Made-with: Cursor

gitops/argocd/jsonpatch-multisource.json

@@ -0,0 +1,23 @@
+[
+  {"op": "remove", "path": "/spec/source"},
+  {"op": "add", "path": "/spec/sources", "value": [
+    {
+      "repoURL": "https://git.luneski.fr/luneski/onelab-k8s.git",
+      "targetRevision": "main",
+      "path": "gitops/charts/onelab",
+      "helm": {
+        "releaseName": "onelab",
+        "valueFiles": ["../../values/k3s-example.yaml"]
+      }
+    },
+    {
+      "repoURL": "https://git.luneski.fr/luneski/onelab-k8s.git",
+      "targetRevision": "main",
+      "path": "gitops/observability",
+      "helm": {
+        "releaseName": "onelab-obs",
+        "valueFiles": ["values.yaml"]
+      }
+    }
+  ]}
+]