Add day selector

Days/Day1.cs

@@ -0,0 +1,14 @@
+using Spectre.Console;
+
+namespace AdventOfCode.Days;
+
+public class Day1 : Day
+{
+    public override int Number => 1;
+    public override string Name => "First day";
+
+    public override void Run()
+    {
+        AnsiConsole.WriteLine("Day 1 result");
+    }
+}