feat: persistent player vehicles

[Manason]

fixes #567

Implements design as described in #567

• Tested
• persistence is disabled by default, requires convar to opt-in.
• Changed places where we delete a vehicle in core to use the new core export.
• We'll need to change other Qbox resources to use the DeleteVehicle export to delete vehicles. This export allows the vehicle to be deleted without being respawned by persistence and works even if persistence is disabled via convar.

Adds new exports

• EnablePersistence
• DisablePersistence
• DeleteVehicle

[mafewtm]

I don't think qbx_core should be dependent on qbx_vehicles

[Manason]

I don't think qbx_core should be dependent on qbx_vehicles

qbx_vehicles is an API resource so I think it's fine to depend on it. The alternative is to make qbx_vehicles have a client component instead of server o Lu. Do you think that would be better?

[D4isDAVID]

Should we maybe also warp passengers back to the new vehicle?

[Manason]

Should we maybe also warp passengers back to the new vehicle?

Done. Still need to test this however.