Add collector role

Sets up prometheus to pull metrics, with telegraf to process SNMP data.

roles/collector/files/telegraf.nft

@@ -0,0 +1,9 @@
+table inet filter {
+    chain output {
+        type filter hook output priority 0; policy accept;
+
+        skuid telegraf ct state { established, related } accept
+        skuid telegraf th dport snmp accept
+        skuid telegraf drop
+    }
+}