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/examples/gateway_example.cpp

@@ -0,0 +1,64 @@
+#include <chrono>
+#include <iostream>
+#include <memory>
+#include <string>
+#include <thread>
+
+#include "prometheus/client_metric.h"
+#include "prometheus/counter.h"
+#include "prometheus/family.h"
+#include "prometheus/gateway.h"
+#include "prometheus/registry.h"
+
+#ifdef _WIN32
+#include <Winsock2.h>
+#else
+#include <unistd.h>
+#endif
+
+static std::string GetHostName() {
+  char hostname[1024];
+
+  if (::gethostname(hostname, sizeof(hostname))) {
+    return {};
+  }
+  return hostname;
+}
+
+int main() {
+  using namespace prometheus;
+
+  // create a push gateway
+  const auto labels = Gateway::GetInstanceLabel(GetHostName());
+
+  Gateway gateway{"127.0.0.1", "9091", "sample_client", labels};
+
+  // create a metrics registry with component=main labels applied to all its
+  // metrics
+  auto registry = std::make_shared<Registry>();
+
+  // add a new counter family to the registry (families combine values with the
+  // same name, but distinct label dimensions)
+  auto& counter_family = BuildCounter()
+                             .Name("time_running_seconds_total")
+                             .Help("How many seconds is this server running?")
+                             .Labels({{"label", "value"}})
+                             .Register(*registry);
+
+  // add a counter to the metric family
+  auto& second_counter = counter_family.Add(
+      {{"another_label", "value"}, {"yet_another_label", "value"}});
+
+  // ask the pusher to push the metrics to the pushgateway
+  gateway.RegisterCollectable(registry);
+
+  for (;;) {
+    std::this_thread::sleep_for(std::chrono::seconds(1));
+    // increment the counter by one (second)
+    second_counter.Increment();
+
+    // push metrics
+    auto returnCode = gateway.Push();
+    std::cout << "returnCode is " << returnCode << std::endl;
+  }
+}