fix: updated ui error rate prom rule

Author: henrywhitaker3

argo/cluster/monitoring/kube-prometheus-stack/chart/rules/srep.yaml

@@ -7,7 +7,10 @@ spec:
     - name: ui
       rules:
         - alert: UIErrorRate
-          expr: ((rate(srep_ui_requests_total_count{status=~"2..|4..|3.."}[1m]) / rate(srep_ui_requests_total_count[1m])) * 100) < 99.99
+          expr: |
+            ((sum(rate(srep_ui_requests_total_count{code=~"2..|4..|3.."}[1m]) or vector(0))
+              /
+            sum(rate(srep_ui_requests_total_count[1m]) or vector(0))) * 100) < 99.99
           for: 1m
           labels:
             severity: critical