Tidy up precipitation (#3023)

Fixes #2953

This is an attempt to fix the issue with precipitation amount and
percentage mixup. I have created a separate
`precipitationPercentage`-variable where the probability of rain can be
stored.

The config options now has the old `showPrecipitationAmount` in addition
to a new setting: `showPrecipitationProbability` (shows the likelihood
of rain).

<details>
  <summary>Examples</summary>
  
  ### Yr

I tested the Yr weather provider for a Norwegian city Bergen that has a
lot of rain. I have removed properties that are irrelevant for this demo
from the config-samples below.

Config:
  ```js
{
	module: "weather",
	config: {
			weatherProvider: "yr",
			type: "current",
			showPrecipitationAmount: true,
			showPrecipitationProbability: true
	}
},
{
	module: "weather",
	config: {
			weatherProvider: "yr",
			type: "hourly",
			showPrecipitationAmount: true,
			showPrecipitationProbability: true
	}
},
{
	module: "weather",
	config: {
			weatherProvider: "yr",
			type: "daily",
			showPrecipitationAmount: true,
			showPrecipitationProbability: true
	}
}
  ```

Result:<br/>
<img width="444" alt="screenshot"
src="https://user-images.githubusercontent.com/34011212/216775423-4e37345c-f915-47e5-8551-7c544ebd24b1.png">

</details>

---------

Co-authored-by: Magnus Marthinsen <magmar@online.no>
Co-authored-by: Veeck <github@veeck.de>

modules/default/weather/providers/weatherflow.js

@@ -55,6 +55,7 @@ WeatherProvider.register("weatherflow", {
 					weather.date = moment.unix(forecast.day_start_local);
 					weather.minTemperature = forecast.air_temp_low;
 					weather.maxTemperature = forecast.air_temp_high;
+					weather.precipitationProbability = forecast.precip_probability;
 					weather.weatherType = forecast.icon;
 					weather.snow = 0;