Parametrize mcp_docker_registry host

Related-Bug: PROD-22480 (PROD:22480)

Change-Id: I36ad55a1960f6c8e025d9c967bbc7658927fc872
diff --git a/docker/swarm/stack/monitoring/alerta.yml b/docker/swarm/stack/monitoring/alerta.yml
index 5e99286..8c9d7aa 100644
--- a/docker/swarm/stack/monitoring/alerta.yml
+++ b/docker/swarm/stack/monitoring/alerta.yml
@@ -2,7 +2,8 @@
 - system.prometheus.alerta
 parameters:
   _param:
-    docker_image_alerta: docker-prod-local.artifactory.mirantis.com/mirantis/external/alerta-web:latest
+    mcp_docker_registry: 'docker-prod-local.artifactory.mirantis.com'
+    docker_image_alerta: ${_param:mcp_docker_registry}/mirantis/external/alerta-web:latest
     alerta_mongodb_uri: "mongodb://${_param:cluster_node01_address}:27017,${_param:cluster_node02_address}:27017,${_param:cluster_node03_address}:27017/alerta?replicaSet=stacklight"
     alerta_admin_username: "admin@alerta.io"
   docker: