Add filtering for notification receivers

Set default filtering regexes for email, slack
and pushkin. Set param prometheus_server_alert_label_route
to include all current receivers.

PROD-18981

Change-Id: Ia58914db427bf3249ae12d7bf02f4dd36bb277dc
diff --git a/prometheus/alertmanager/notification/pushkin.yml b/prometheus/alertmanager/notification/pushkin.yml
index 151801b..ec749d7 100644
--- a/prometheus/alertmanager/notification/pushkin.yml
+++ b/prometheus/alertmanager/notification/pushkin.yml
@@ -10,6 +10,9 @@
           routes:
             pushkin:
               receiver: HTTP-pushkin
+              match_re:
+                - label: route
+                  value: '(.*pushkin.*)'
               continue: true
         receiver:
           HTTP-pushkin: