Adds a callGamemodeFunction invoke for when the client is done loading the mission so the gamemode can do stuff once the player is done loading, but before fully connecting/spawning in

Templates/BaseGame/game/core/clientServer/scripts/client/levelDownload.tscript

@@ -274,6 +274,8 @@ function sceneLightingComplete()
    
    onPhaseComplete("STARTING MISSION");
    
+   callGamemodeFunction("onClientMissionLoaded");
+   
    // The is also the end of the mission load cycle.
    commandToServer('MissionStartPhase3Ack', $MSeq);
 }