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>

tests/configs/modules/weather/forecastweather_units.js

@@ -15,7 +15,8 @@ let config = {
 				location: "Munich",
 				mockData: '"#####WEATHERDATA#####"',
 				weatherEndpoint: "/forecast/daily",
-				decimalSymbol: "_"
+				decimalSymbol: "_",
+				showPrecipitationAmount: true
 			}
 		}
 	]

tests/configs/modules/weather/hourlyweather_showPrecipitation.js

@@ -0,0 +1,27 @@
+/* MagicMirror² Test config hourly weather
+ *
+ * By rejas https://github.com/rejas
+ * MIT Licensed.
+ */
+let config = {
+	timeFormat: 12,
+
+	modules: [
+		{
+			module: "weather",
+			position: "bottom_bar",
+			config: {
+				type: "hourly",
+				location: "Berlin",
+				mockData: '"#####WEATHERDATA#####"',
+				showPrecipitationAmount: true,
+				showPrecipitationProbability: true
+			}
+		}
+	]
+};
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = config;
+}