Add initial entity and migration for MissionLaunch

src/MissionControl.Domain/Entities/Mission.cs

@@ -11,4 +11,6 @@ public class Mission
     public MissionStatus Status { get; set; } = MissionStatus.Planned;
 
     public DateTimeOffset CreatedAt { get; init; } = DateTimeOffset.UtcNow;
+
+    public MissionLaunch? MissionLaunch { get; set; }
 }