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 499ed6d95e.

* 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>

controller/PostgreSQL.hpp

@@ -26,6 +26,8 @@
 #include <memory>
 #include <redis++/redis++.h>
 
+#include "../node/Metrics.hpp"
+
 extern "C" {
 typedef struct pg_conn PGconn;
 }
@@ -53,6 +55,7 @@ public:
 	}
 
 	virtual std::shared_ptr<Connection> create() {
+		Metrics::conn_counter++;
 		auto c = std::shared_ptr<PostgresConnection>(new PostgresConnection());
 		c->c = std::make_shared<pqxx::connection>(m_connString);
 		return std::static_pointer_cast<Connection>(c);