Add prometheus metrics for Central controllers (#1969)

* add header-only prometheus lib to ext

* rename folder

* Undo rename directory

* prometheus simpleapi included on mac & linux

* wip

* wire up some controller stats

* Get windows building with prometheus

* bsd build flags for prometheus

* Fix multiple network join from environment entrypoint.sh.release (#1961)

* _bond_m guards _bond, not _paths_m (#1965)

* Fix: warning: mutex '_aqm_m' is not held on every path through here [-Wthread-safety-analysis] (#1964)

* Serve prom metrics from /metrics endpoint

* Add prom metrics for Central controller specific things

* reorganize metric initialization

* testing out a labled gauge on Networks

* increment error counter on throw

* Consolidate metrics definitions

Put all metric definitions into node/Metrics.hpp.  Accessed as needed
from there.

* Revert "testing out a labled gauge on Networks"

This reverts commit 499ed6d95e11452019cdf48e32ed4cd878c2705b.

* still blows up but adding to the record for completeness right now

* Fix runtime issues with metrics

* Add metrics files to visual studio project

* Missed an "extern"

* add copyright headers to new files

* Add metrics for sent/received bytes (total)

* put /metrics endpoint behind auth

* sendto returns int on Win32

---------

Co-authored-by: Leonardo Amaral <leleobhz@users.noreply.github.com>
Co-authored-by: Brenton Bostick <bostick@gmail.com>

ext/prometheus-cpp-lite-1.0/core/include/prometheus/builder.h

@@ -0,0 +1,35 @@
+#pragma once
+
+#include <string>
+#include <map>
+#include "registry.h"
+
+namespace prometheus {
+
+  template <typename CustomMetric>
+  class Builder {
+
+    Family::Labels labels_;
+    std::string name_;
+    std::string help_;
+
+  public:
+    Builder& Labels(const std::map<const std::string, const std::string>& labels) {
+      labels_ = labels;
+      return *this;
+    }
+    Builder& Name(const std::string& name) {
+      name_ = name;
+      return *this;
+    }
+    Builder& Help(const std::string& help) {
+      help_ = help;
+      return *this;
+    }
+    CustomFamily<CustomMetric>& Register(Registry& registry) {
+      return registry.Add<CustomFamily<CustomMetric>>(name_, help_, labels_);
+    }
+
+  };
+
+}