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>

tests/unit/functions/weather_object_spec.js

@@ -10,7 +10,7 @@ describe("WeatherObject", () => {
 	beforeAll(() => {
 		originalTimeZone = moment.tz.guess();
 		moment.tz.setDefault("Africa/Dar_es_Salaam");
-		weatherobject = new WeatherObject("metric", "metric", "metric", true);
+		weatherobject = new WeatherObject();
 	});
 
 	it("should return true for daytime at noon", () => {
@@ -25,6 +25,14 @@ describe("WeatherObject", () => {
 		expect(weatherobject.isDayTime()).toBe(false);
 	});
 
+	it("should convert windspeed correctly from mph to mps", () => {
+		expect(Math.round(weatherobject.convertWindToMetric(93.951324266285))).toBe(42);
+	});
+
+	it("should convert wind direction correctly from cardinal to value", () => {
+		expect(weatherobject.valueWindDirection("SSE")).toBe(157);
+	});
+
 	afterAll(() => {
 		moment.tz.setDefault(originalTimeZone);
 	});