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/slack.yml b/prometheus/alertmanager/notification/slack.yml
index 412e91f..a86c403 100644
--- a/prometheus/alertmanager/notification/slack.yml
+++ b/prometheus/alertmanager/notification/slack.yml
@@ -7,6 +7,9 @@
           routes:
             slack:
               receiver: HTTP-slack
+              match_re:
+                - label: route
+                  value: '(.*slack.*)'
               continue: true
         receiver:
           HTTP-slack: