Decrease Pushgateway replicas number

Pushgateway doesn't support clustering - as a result, we have all
metrics split to 2 pieces without replica control.

Change-Id: I1de7d2428e67df6a309bbfeb402bab0ea0e2956c
Related-PROD: PROD-31805
(cherry picked from commit 3ad9c9657624f175a865c8f94d5fd0256049fa66)
diff --git a/docker/swarm/stack/monitoring/pushgateway.yml b/docker/swarm/stack/monitoring/pushgateway.yml
index 461eb0b..582dc93 100644
--- a/docker/swarm/stack/monitoring/pushgateway.yml
+++ b/docker/swarm/stack/monitoring/pushgateway.yml
@@ -15,7 +15,7 @@
               networks:
                 - monitoring
               deploy:
-                replicas: 2
+                replicas: 1
                 labels:
                   com.mirantis.monitoring: "pushgateway"
                 restart_policy: