Update ghcr.io/twin/gatus Docker tag to v5.20.0 (#869)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [ghcr.io/twin/gatus](https://github.com/TwiN/gatus) | minor | `v5.19.0` -> `v5.20.0` |

---

### Release Notes

<details>
<summary>TwiN/gatus (ghcr.io/twin/gatus)</summary>

### [`v5.20.0`](https://github.com/TwiN/gatus/releases/tag/v5.20.0)

[Compare Source](https://github.com/TwiN/gatus/compare/v5.19.0...v5.20.0)

#### What's Changed

- feat(api): Add optional duration to external endpoint results by [@&#8203;bcross](https://github.com/bcross) in https://github.com/TwiN/gatus/pull/1092
- fix: Limit the pageSize to maximum-number-of-results on first page by [@&#8203;TwiN](https://github.com/TwiN) in https://github.com/TwiN/gatus/pull/1149
- fix: Convert key to lowercase when looking up endpoint by key by [@&#8203;TwiN](https://github.com/TwiN) in https://github.com/TwiN/gatus/pull/1150

#### New Contributors

- [@&#8203;bcross](https://github.com/bcross) made their first contribution in https://github.com/TwiN/gatus/pull/1092

**Full Changelog**: https://github.com/TwiN/gatus/compare/v5.19.0...v5.20.0

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

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

♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

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

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
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Reviewed-on: #869
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

clusters/cl01tl/monitoring/gatus/values.yaml

@@ -7,7 +7,7 @@ gatus:
     enabled: true
   image:
     repository: ghcr.io/twin/gatus
-    tag: v5.19.0
+    tag: v5.20.0
   annotations:
     reloader.stakater.com/auto: "true"
   service: