Add custom fact file for `hw_counters` fact in telegraf role

roles/telegraf/files/hw_counters.fact

+#!/usr/bin/python3
+
+import json
+import os
+
+def render_data(data):
+    return json.dumps(data)
+
+device_name = 'mlx5_0'
+hw_counters = {}
+path = '/sys/class/infiniband/{}/ports/1/hw_counters/'.format(device_name)
+
+hw_counters[device_name] = os.listdir(path)
+
+print(render_data(hw_counters))
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