Get back environment label for alerta alerts

Change-Id: I113c80641a3e1929240ec47b06ca1500c8f7b727
Related-PROD: PROD-24968 (PROD:24968)
diff --git a/prometheus/server/alert/alerta_relabel.yml b/prometheus/server/alert/alerta_relabel.yml
index 1e06b6c..63ed20a 100644
--- a/prometheus/server/alert/alerta_relabel.yml
+++ b/prometheus/server/alert/alerta_relabel.yml
@@ -1,8 +1,13 @@
 parameters:
+  _param:
+    alerta_environment_label: ${_param:cluster_domain}
   prometheus:
     server:
       config:
         alert_relabel_configs:
+          - replacement: "${_param:alerta_environment_label}"
+            source_labels: "environment"
+            target_label: "environment"
           - replacement: "aggregated"
             source_labels: "instance"
             target_label: "instance"