Add prometheus weathermen exporter

[lstrojny]

A multi provider weather exporter written in Rust (https://github.com/lstrojny/prometheus-weathermen)

Example output:

# HELP weather_temperature_celsius prometheus-weathermen temperature.
# TYPE weather_temperature_celsius gauge
# UNIT weather_temperature_celsius celsius
weather_temperature_celsius{version="0.3.0",source="de.dwd",location="Home",city="München-Stadt",latitude="…",longitude="…"} 8.399999618530274
weather_temperature_celsius{version="0.3.0",source="org.openweathermap",location="Home",city="Altstadt",latitude="…",longitude="…"} 7.1199951171875
# HELP weather_relative_humidity_ratio prometheus-weathermen relative humidity.
# TYPE weather_relative_humidity_ratio gauge
# UNIT weather_relative_humidity_ratio ratio
weather_relative_humidity_ratio{version="0.3.0",source="org.openweathermap",location="Home",city="Altstadt",latitude="…",longitude="…"} 0.6
weather_relative_humidity_ratio{version="0.3.0",source="de.dwd",location="Home",city="München-Stadt",latitude="…",longitude="…"} 0.522
# EOF