[Zones] Convert IDLE_WHEN_EMPTY to a Zone Column (#3891)

* [Rules] Convert IDLE_WHEN_EMPTY to a rule

# Notes
- Converts `IDLE_WHEN_EMPTY` to `Zone:ZonesIdleWhenEmpty` so that we can change this on the fly or on a zone-by-zone basis instead of having to recompile to do this.
- Especially helpful for those using release binaries that do not compile their own source.

* Convert to zone column.

* Update ruletypes.h

* Update ruletypes.h

* Update entity.cpp

* Update entity.cpp

* Rename.

* Update database_update_manifest.cpp

* Update base_zone_repository.h

* Update zone.cpp

* seconds_before_idle

* Update database_update_manifest.cpp

* Getter/Setters/Private

* Update base_zone_repository.h

* IsIdle()/SetIsIdle()

* Update entity.cpp

zone/questmgr.cpp

@@ -933,12 +933,13 @@ void QuestManager::repopzone() {
 	}
 }
 
-void QuestManager::processmobswhilezoneempty(bool on) {
-	if(zone) {
-		zone->process_mobs_while_empty = on;
-	}
-	else {
-		LogQuests("QuestManager::processmobswhilezoneempty called with nullptr zone. Probably syntax error in quest file");
+void QuestManager::processmobswhilezoneempty(bool idle_when_empty) {
+	if (zone) {
+		zone->SetIdleWhenEmpty(idle_when_empty);
+	} else {
+		LogQuests(
+			"QuestManager::processmobswhilezoneempty called with nullptr zone. Probably syntax error in quest file"
+		);
 	}
 }