Add stats haproxy module to alert exceptions

Change-Id: I50e156944bc86a3bbc40998c26a8fad2a4d8116d
PROD-related: PROD-33756
diff --git a/haproxy/meta/prometheus.yml b/haproxy/meta/prometheus.yml
index d6b96a1..cd3e950 100644
--- a/haproxy/meta/prometheus.yml
+++ b/haproxy/meta/prometheus.yml
@@ -61,8 +61,8 @@
         description: "{{ $value }} {{ $labels.proxy }} back ends (>= 50%) are down."
     HaproxyBackendOutage:
       if: >-
-        max(haproxy_active_servers{sv="BACKEND"}) by (proxy)
-        + max(haproxy_backup_servers{sv="BACKEND"}) by (proxy) == 0
+        max(haproxy_active_servers{sv="BACKEND", proxy!="stats"}) by (proxy)
+        + max(haproxy_backup_servers{sv="BACKEND", proxy!="stats"}) by (proxy) == 0
       labels:
         severity: critical
         service: haproxy