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/collectable.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <vector>
+
+#include "prometheus/metric_family.h"
+
+namespace prometheus {
+
+  /// @brief Interface implemented by anything that can be used by Prometheus to
+  /// collect metrics.
+  ///
+  /// A Collectable has to be registered for collection. See Registry.
+  class Collectable {
+
+    public:
+
+      //Collectable() = default;
+
+      virtual ~Collectable() = default;
+
+      using MetricFamilies = std::vector<MetricFamily>;
+
+      /// \brief Returns a list of metrics and their samples.
+      virtual MetricFamilies Collect() const = 0;
+  };
+
+}  // namespace prometheus