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

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

code/components/jomjol_flowcontroll/ClassFlowControll.h

@@ -52,6 +52,7 @@ public:
 	string GetPrevalue(std::string _number = "");	
 	bool ReadParameter(FILE* pfile, string& aktparamgraph);	
 	string getJSON();
+	const std::vector<NumberPost*> &getNumbers();
 	string getNumbersName();
 
 	string TranslateAktstatus(std::string _input);