Core/Events: allow to override holiday durations and correct Lunar Festival duration down to 2 weeks

* the new field must be set for every new holiday date entry to take effect if you want to override the duration of the given

sql/updates/world/custom/custom_2020_01_11_05_world.sql

@@ -0,0 +1,2 @@
+ALTER TABLE `holiday_dates` ADD COLUMN `holiday_duration` INT(10) UNSIGNED NOT NULL AFTER `date_value`;
+UPDATE `holiday_dates` SET `holiday_duration`= 360 WHERE `id`= 327;

src/server/game/Events/GameEventMgr.cpp

@@ -945,8 +945,8 @@ void GameEventMgr::LoadHolidayDates()
 {
     uint32 oldMSTime = getMSTime();
 
-    //                                               0   1         2
-    QueryResult result = WorldDatabase.Query("SELECT id, date_id, date_value FROM holiday_dates");
+    //                                               0   1         2          3
+    QueryResult result = WorldDatabase.Query("SELECT id, date_id, date_value, holiday_duration FROM holiday_dates");
     if (!result)
     {
         TC_LOG_INFO("server.loading", ">> Loaded 0 holiday dates. DB table `holiday_dates` is empty.");
@@ -972,6 +972,9 @@ void GameEventMgr::LoadHolidayDates()
         }
         entry->Date[dateId] = fields[2].GetUInt32();
 
+        if (uint32 duration = fields[3].GetUInt32())
+            entry->Duration[0] = duration;
+
         auto itr = std::lower_bound(modifiedHolidays.begin(), modifiedHolidays.end(), entry->Id);
         if (itr == modifiedHolidays.end() || *itr != entry->Id)
             modifiedHolidays.insert(itr, entry->Id);