chore(deps): update helm release kube-prometheus-stack to v81

Author: renovate[bot]

applications/prometheus.yaml

@@ -9,7 +9,7 @@ spec:
     server: "https://kubernetes.default.svc"
   source:
     repoURL: "https://prometheus-community.github.io/helm-charts"
-    targetRevision: 75.18.1
+    targetRevision: 81.2.1
     chart: kube-prometheus-stack
     helm:
       values: |