Add new electricity price provider: Energy-Charts #381 (#590)

* feat(ElecPriceEnergyCharts): Add new electricity price provider: Energy-Charts

* feat(ElecPriceEnergyCharts): update data only if needed

* test(elecpriceforecast): add test for energycharts

* docs(predictions.md): add ElecPriceEnergyCharts Provider

Signed-off-by: redmoon2711 <redmoon2711@gmx.de>

docs/akkudoktoreos/prediction.md

@@ -119,6 +119,7 @@ Configuration options:
   - `provider`: Electricity price provider id of provider to be used.
 
     - `ElecPriceAkkudoktor`: Retrieves from Akkudoktor.net.
+    - `ElecPriceEnergyCharts`: Retrieves from Energy-Charts.info.
     - `ElecPriceImport`: Imports from a file or JSON string.
 
   - `charges_kwh`: Electricity price charges (€/kWh).
@@ -133,6 +134,14 @@ prices by extrapolating historical price data combined with the most recent actu
 from Akkudoktor.net. Electricity price charges given in the `charges_kwh` configuration
 option are added.
 
+### ElecPriceEnergyCharts Provider
+
+The `ElecPriceEnergyCharts` provider retrieves electricity prices directly from **Energy-Charts.info**,
+which supplies price data for the next 24 hours. For periods beyond 24 hours, the provider generates
+prices by extrapolating historical price data combined with the most recent actual prices obtained
+from Energy-Charts.info. Electricity price charges specified in the `charges_kwh` configuration option
+are included in the calculation as `(market price + charges_kwh) * 1.19 VAT`.
+
 ### ElecPriceImport Provider
 
 The `ElecPriceImport` provider is designed to import electricity prices from a file or a JSON