New datasink class CSVSink

This is a follow-up on MR 102 and MR 104.

A new sink class is added CSVSink. Instead of printing the measurement to the console, the measurement is printed to a CSV file.

The example is run as ./build/bin/ps_monitor src/config/input-hw.json File low-voltage

The format in the output file similar to that of ConsoleSink except the tags are columns and the first column is empty. The file is saved as powersupply.csv, where powersupply is the name of the measurement.

time,Channel,Voltage,Current
1595909424445, low-voltage,0.000434768,0.000304329
1595909424633, low-voltage,0.000582471,0.000284497
1595909424809, low-voltage,0.000631706,0.000324161

The sink and the name for the output directory are specified in the configuration json:

    "datasinks":{
        "File":{
            "sinktype": "CSVSink",
            "directory": "./"
        }