refactor: models use guids as PKs now

Models/Database/PlayerMission.cs

@@ -2,10 +2,10 @@ namespace GamificationService.Models.Database;
 
 public class PlayerMission
 {
-    public long Id { get; set; }
-    public long PlayerId { get; set; }
+    public Guid Id { get; set; }
+    public Guid PlayerId { get; set; }
     public required Player Player { get; set; }
-    public long MissionId { get; set; }
+    public Guid MissionId { get; set; }
     public required Mission Mission { get; set; }
     public DateTime? Completed { get; set; }
     public DateTime? RewardsRedeemed { get; set; }