Core/Players: Introduce configurable allied race starting level and fix default level selection for pandaren death knights

Port From (https://github.com/TrinityCore/TrinityCore/commit/bff8f2ff4ebc4144a2c1c31a65b78a1f0ed3f973)

Source/Framework/Constants/CliDBConst.cs

@@ -991,6 +991,11 @@ namespace Framework.Constants
         Factional = 0x40
     }
 
+    public enum ChrRacesFlag
+    {
+        AlliedRace = 0x80000
+    }
+
     public enum ChrSpecializationFlag
     {
         Caster = 0x01,

Source/Framework/Constants/SharedConst.cs

@@ -1346,6 +1346,7 @@ namespace Framework.Constants
         SkipCinematics,
         SocketTimeoutTime,
         SocketTimeoutTimeActive,
+        StartAlliedRaceLevel,
         StartAllExplored,
         StartAllRep,
         StartAllSpells,