feat(container): update image ghcr.io/twin/gatus to v5.15.0 (#1174)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| ghcr.io/twin/gatus | minor | `v5.14.0` -> `v5.15.0` |

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kubernetes/apps/monitoring/gatus/app/helmrelease.yaml

@@ -53,7 +53,7 @@ spec:
           app:
             image:
               repository: ghcr.io/twin/gatus
-              tag: v5.14.0
+              tag: v5.15.0
             env:
               TZ: ${TIMEZONE}
               GATUS_CONFIG_PATH: /config