More strict matching and small text change on the alert

alerts/worker-down.rules

 ALERT FrontEndWorkerDown
-  IF min(up{fqdn=~"worker-(web|ssh|api|kiq)*.*"}) without (job) == 0
+  IF min(up{fqdn=~"worker-(web|ssh|api|kiq)[0-9]+.fe.gitlab.com"}) without (job) == 0
   FOR 5m
   LABELS {severity="critical", pager="pagerduty"}
   ANNOTATIONS {
     title="Front end worker {{$labels.instance}} host is down",
-    description="One of front end web workers is down for more than 5 minutes, this results in a degraded performance of GitLab.com",
+    description="One of front end node is down for more than 5 minutes, this results in a degraded performance of GitLab.com",
     runbook="troubleshooting/worker-down.md"
   }