Add collector role

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

roles/collector/README.md

@@ -0,0 +1,18 @@
+Set up metric collection with prometheus and telegraf as the SNMP proxy.
+
+NetBox config context should contain the lists `prometheus_hosts` and `snmp_hosts` with job definitions. Each entry should define `name` and `nb_filter` user to query hosts from NetBox. For example:
+
+    {
+        "prometheus_hosts": [
+            {
+                "name": "classroom",
+                "nb_filter": "role=desktop-computer status=active location=classroom"
+            }
+        ],
+        "snmp_hosts": [
+            {
+                "name": "switch",
+                "nb_filter": "role=switch name__isw=sw- status=active status=staged status=planned"
+            }
+        ]
+    }