feat(helm): update chart loki to 5.20.0 (#2371)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [loki](https://grafana.github.io/helm-charts)
([source](https://togithub.com/grafana/helm-charts)) | minor | `5.19.0`
-> `5.20.0` |

---

### Release Notes

<details>
<summary>grafana/helm-charts (loki)</summary>

###
[`v5.20.0`](https://togithub.com/grafana/helm-charts/releases/tag/helm-loki-5.20.0)

Helm chart for Grafana Loki in simple, scalable mode

Source commit:
grafana/loki@bfe558c

Tag on source:
https://github.com/grafana/loki/releases/tag/helm-loki-5.20.0

</details>

---

### Configuration

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Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you
are satisfied.

♻ **Rebasing**: Whenever PR becomes conflicted, or you tick the
rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update
again.

---

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---

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kubernetes/apps/monitoring/loki/app/helm-release.yaml

@@ -9,7 +9,7 @@ spec:
   chart:
     spec:
       chart: loki
-      version: 5.19.0
+      version: 5.20.0
       sourceRef:
         kind: HelmRepository
         name: grafana-charts