feat(prometheus-exporter): add metrics-pole for power metrics

prometheus-exporter/utils/prometheus.lua

@@ -0,0 +1,16 @@
+local M = {}
+
+--- Formats a name + table of labels as a Prometheus metric
+--- @param name string
+--- @param labels table
+--- @param value number
+function M.counter(name, labels, value)
+    local label_parts = {}
+    for k, v in pairs(labels) do
+        table.insert(label_parts, string.format('%s="%s"', k, v))
+    end
+    local label_str = table.concat(label_parts, ",")
+    return string.format("factorio_%s_total{%s} %d", name, label_str, value)
+end
+
+return M