gatus: let Argo CD prune old resources

configMapGenerator gives every config change a new gatus-config-<hash> ConfigMap, and without prune the old one stayed behind and left the app OutOfSync.

apps/templates/gatus-folder.yaml

@@ -18,4 +18,7 @@ spec:
     syncOptions:
     - CreateNamespace=true
     automated:
+      # Each config change generates a new gatus-config-<hash> ConfigMap;
+      # prune removes the old one.
+      prune: true
       selfHeal: true