Use metric units internally in all weatherproviders (#2849)

So finally I think this refactorin is ready to be reviewed :-)

DONE:
- [x] Removed all conversion functions for wind and temperature from
specific weatherproviders
- [x] Use internally only metric units: celsius for temperature, meters
per seconds for wind
- [x] Convert temp and wind into the configured units when displaying
data on the UI
- [x] look how beaufort calculation uses metrics, added knots as new
windunit
- [x] add more e2e tests 

Checked providers:
- [x] Darksky
- [x] EnvCanada
- [x] OpenWeatherMap
- [x] SMHI provider 
- [x] UK Met Office
- [x] UK Met Office DataHub
- [x] WeatherBit
- [x] WeatherFlow
- [x] WeatherGov

TODO in different tickets:
- check weatherproviders for usage of weatherEndpoint (as seen in
https://github.com/MichMich/MagicMirror-Documentation/issues/131) -> see
#2926
- cleanup precipations -> #2953

Co-authored-by: veeck <michael@veeck.de>

modules/default/weather/providers/weatherbit.js

@@ -23,11 +23,6 @@ WeatherProvider.register("weatherbit", {
 		lon: 0
 	},
 
-	units: {
-		imperial: "I",
-		metric: "M"
-	},
-
 	fetchedLocation: function () {
 		return this.fetchedLocationName || "";
 	},
@@ -95,8 +90,7 @@ WeatherProvider.register("weatherbit", {
 
 	// Create a URL from the config and base URL.
 	getUrl() {
-		const units = this.units[this.config.units] || "auto";
-		return `${this.config.apiBase}${this.config.weatherEndpoint}?lat=${this.config.lat}&lon=${this.config.lon}&units=${units}&key=${this.config.apiKey}`;
+		return `${this.config.apiBase}${this.config.weatherEndpoint}?lat=${this.config.lat}&lon=${this.config.lon}&units=M&key=${this.config.apiKey}`;
 	},
 
 	// Implement WeatherDay generator.
@@ -106,7 +100,7 @@ WeatherProvider.register("weatherbit", {
 		let tzOffset = d.getTimezoneOffset();
 		tzOffset = tzOffset * -1;
 
-		const currentWeather = new WeatherObject(this.config.units, this.config.tempUnits, this.config.windUnits);
+		const currentWeather = new WeatherObject();
 
 		currentWeather.date = moment.unix(currentWeatherData.data[0].ts);
 		currentWeather.humidity = parseFloat(currentWeatherData.data[0].rh);
@@ -126,7 +120,7 @@ WeatherProvider.register("weatherbit", {
 		const days = [];
 
 		for (const forecast of forecasts) {
-			const weather = new WeatherObject(this.config.units, this.config.tempUnits, this.config.windUnits);
+			const weather = new WeatherObject();
 
 			weather.date = moment(forecast.datetime, "YYYY-MM-DD");
 			weather.minTemperature = forecast.min_temp;