Allows for the cookie to be passed as an env variable

Author: pBouillon

src/AdventOfCode.Commons/Configuration.cs

@@ -8,9 +8,10 @@ public static class Configuration
     /// <summary>
     /// Your session cookie, if you want to retrieve your input from the internet
     /// </summary>
+    ///
     /// <remarks>
     /// To get your cookie, head to https://adventofcode.com/, then look into the cookies
     /// the website has set and paste its value here, it be something like <c>session:"[value]"</c>
     /// </remarks>
-    public const string? CookieValue = null;
+    public readonly static string? CookieValue = Environment.GetEnvironmentVariable("AOC_COOKIE");
 }