L2SS-1971: Use notification template for alarm messages

Closes L2SS-1971

alerting/cp.yaml

@@ -6,7 +6,7 @@ contactPoints:
       - uid: slackalarms
         type: slack
         settings:
-          title: '{{ externalURL }}: {{ template "slack.default.title" }}'
+          title: '{{ template "host.title" .}}'
           recipient: C07BT0TAFRR  # Slack channel ID
           # Dummy token replaced by scripts
           token: "xoxb-noop"