[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

common/version.h

@@ -42,7 +42,7 @@
  * Manifest: https://github.com/EQEmu/Server/blob/master/utils/sql/db_update_manifest.txt
  */
 
-#define CURRENT_BINARY_DATABASE_VERSION 9251
+#define CURRENT_BINARY_DATABASE_VERSION 9252
 
 #define CURRENT_BINARY_BOTS_DATABASE_VERSION 9041