add Prometheus/OpenMetrics exporter (#3081)

* add prometheus endpoint

* refine metrics implementation

* move metrics generator to ClassFlowControll

* add more metrics
align prefix

* add more metrics
clean up

* refine documentation

* revert dependencies change

* sanitize labels

* create separate module for openmetrics

* move openmetrics to separate folder

* clean up

* add basic unit-tests

* work with const numbers
add replaceAll for string replacement
avoid opening std namespace
adapt unit-tests

* Update code/main/server_main.cpp

---------

Co-authored-by: CaCO3 <caco3@ruinelli.ch>

code/components/openmetrics/openmetrics.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#ifndef OPENMETRICS_H
+#define OPENMETRICS_H
+
+#include <string>
+#include <fstream>
+#include <vector>
+
+#include "ClassFlowDefineTypes.h"
+
+std::string createMetric(const std::string &metricName, const std::string &help, const std::string &type, const std::string &value);
+std::string createSequenceMetrics(std::string prefix, const std::vector<NumberPost *> &numbers);
+
+#endif // OPENMETRICS_H