[12145] Add new condition CONDITION_COMPLETED_ENCOUNTER

This condition returns true if a DungeonEncounter is done in this map.

value1, value2 are expected to be the IDs from DungeonEncounter(dbc)
value2 is optional, if both values are given, the condition will be true if one of the two DungeonEncounters are done.

Thanks to crackm for testing

src/game/ObjectMgr.h

@@ -389,6 +389,7 @@ enum ConditionType
     // True if player has skill skill_id and skill less than (and not equal) skill_value (for skill_value > 1)
     // If skill_value == 1, then true if player has not skill skill_id
     CONDITION_REPUTATION_RANK_MAX   = 30,                   // faction_id   max_rank
+    CONDITION_COMPLETED_ENCOUNTER   = 31,                   // encounter_id encounter_id2       encounter_id[2] = DungeonEncounter(dbc).id (if value2 provided it will return value1 OR value2)
 };
 
 class PlayerCondition