Added configurable weapons.

AlientAttack.MonoGame/Things/Weapons/WeaponDef.cs

@@ -0,0 +1,11 @@
+using AlienAttack.MonoGame.Things.Bullets;
+
+namespace AlienAttack.MonoGame.Things.Weapons;
+
+public sealed class WeaponDef
+{
+    public required string Name { get; init; }
+    public required ShotPattern Pattern { get; init; }
+    public required BulletDef Bullet { get; init; }
+    public required string FireSfxKey { get; init; } = "player_fire";
+}