Update kube-prometheus-stack Docker tag to v81 (#3279)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [kube-prometheus-stack](https://github.com/prometheus-operator/kube-prometheus) ([source](https://github.com/prometheus-community/helm-charts)) | major | `80.14.4` → `81.0.0` |

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> ⚠️ **Warning**
>
> Some dependencies could not be looked up. Check the Dependency Dashboard for more information.

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### Release Notes

<details>
<summary>prometheus-community/helm-charts (kube-prometheus-stack)</summary>

### [`v81.0.0`](https://github.com/prometheus-community/helm-charts/releases/tag/kube-prometheus-stack-81.0.0)

[Compare Source](https://github.com/prometheus-community/helm-charts/compare/kube-prometheus-stack-80.14.4...kube-prometheus-stack-81.0.0)

kube-prometheus-stack collects Kubernetes manifests, Grafana dashboards, and Prometheus rules combined with documentation and scripts to provide easy to operate end-to-end Kubernetes cluster monitoring with Prometheus using the Prometheus Operator.

#### What's Changed

- \[kube-prometheus-stack] bump prometheus operator to 0.88.0  by [@&#8203;ibakshay](https://github.com/ibakshay) in [#&#8203;6489](https://github.com/prometheus-community/helm-charts/pull/6489)

#### New Contributors

- [@&#8203;ibakshay](https://github.com/ibakshay) made their first contribution in [#&#8203;6489](https://github.com/prometheus-community/helm-charts/pull/6489)

**Full Changelog**: <https://github.com/prometheus-community/helm-charts/compare/kube-prometheus-stack-80.14.4...kube-prometheus-stack-81.0.0>

</details>

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Reviewed-on: #3279
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

clusters/cl01tl/helm/kube-prometheus-stack/Chart.yaml

@@ -20,7 +20,7 @@ maintainers:
   - name: alexlebens
 dependencies:
   - name: kube-prometheus-stack
-    version: 80.14.4
+    version: 81.0.0
     repository: oci://ghcr.io/prometheus-community/charts
   - name: app-template
     alias: ntfy-alertmanager