tf-stage2: set UptimeRobot monitor interval to 300

Our free plan no longer supports 60-second interval for monitors.

tf-stage2/uptimerobot.tf

@@ -35,5 +35,5 @@ resource "uptimerobot_monitor" "uptimerobot_monitor_archlinux" {
   friendly_name = each.key
   type          = "http"
   url           = each.value
-  interval      = 60
+  interval      = 300
 }