upgrade victoria-metrics-k8s-stack 0.48.1 -> 0.81.0 with values migration

otc/observability.buildth.ing/stacks/observability-client/vm-client-stack.yaml

@@ -12,13 +12,14 @@ spec:
       selfHeal: true
     syncOptions:
       - CreateNamespace=true
+      - ServerSideApply=true
   destination:
     name: in-cluster
     namespace: observability
   sources:
     - chart: victoria-metrics-k8s-stack
       repoURL: https://victoriametrics.github.io/helm-charts/
-      targetRevision: 0.48.1
+      targetRevision: 0.81.0
       helm:
         valueFiles:
           - $values/otc/observability.buildth.ing/stacks/observability-client/vm-client-stack/values.yaml