Add game header (#5)

Co-authored-by: Maxime Adler <madler@sqli.com>
Reviewed-on: #5

src/GameIdeas/GameIdeas.Shared/Constants/GlobalConstants.cs

@@ -0,0 +1,7 @@
+namespace GameIdeas.Shared.Constants;
+
+public class GlobalConstants
+{
+    public const string EnterKeyCode = "Enter";
+    public const string PadEnterKeyCode = "NumpadEnter";
+}