Add starter project for Chapter 13

Chapter13/Start/UnoMediaCollection/UnoMediaCollection.DataContracts/WeatherForecast.cs

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+namespace UnoMediaCollection.DataContracts
+{
+    /// <summary>
+    /// A Weather Forecast for a specific date
+    /// </summary>
+    /// <param name="Date">Gets the Date of the Forecast.</param>
+    /// <param name="TemperatureC">Gets the Forecast Temperature in Celsius.</param>
+    /// <param name="Summary">Get a description of how the weather will feel.</param>
+    public record WeatherForecast(DateOnly Date, double TemperatureC, string? Summary)
+    {
+        /// <summary>
+        /// Gets the Forecast Temperature in Fahrenheit
+        /// </summary>
+        public double TemperatureF => 32 + (TemperatureC * 9 / 5);
+    }
+}