[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/ruletypes.h

@@ -338,7 +338,6 @@ RULE_BOOL(Zone, UseZoneController, true, "Enables the ability to use persistent
 RULE_BOOL(Zone, EnableZoneControllerGlobals, false, "Enables the ability to use quest globals with the zone controller NPC")
 RULE_INT(Zone, GlobalLootMultiplier, 1, "Sets Global Loot drop multiplier for database based drops, useful for double, triple loot etc")
 RULE_BOOL(Zone, KillProcessOnDynamicShutdown, true, "When process has booted a zone and has hit its zone shut down timer, it will hard kill the process to free memory back to the OS")
-RULE_INT(Zone, SecondsBeforeIdle, 60, "Seconds before IDLE_WHEN_EMPTY define kicks in")
 RULE_INT(Zone, SpawnEventMin, 3, "When strict is set in spawn_events, specifies the max EQ minutes into the trigger hour a spawn_event will fire. Going below 3 may cause the spawn_event to not fire.")
 RULE_INT(Zone, ForageChance, 25, "Chance of foraging from zone table vs global table")
 RULE_CATEGORY_END()