[Bots] Add attack flag when told to attack (#4490)

This adds a flag to mobs that are told to attack by their owner to prevent unintended attacks.

Previously, if you were to send your bots to attack a target and then switch targets: before casters land their spell or if melee (especially anyone with pets)  hasn't engaged before the target switch, they could switch to your new target and attack.

This adds a flag upon attack and bots will only attack flagged targets.

zone/npc.cpp

@@ -799,6 +799,11 @@ bool NPC::Process()
 		}
 	}
 
+	if (bot_attack_flag_timer.Check()) {
+		bot_attack_flag_timer.Disable();
+		ClearBotAttackFlags();
+	}
+
 	AI_Process();
 
 	return true;